I'm working on modernizing Rosetta Code's infrastructure. Starting with communications. Please accept this time-limited open invite to RC's Slack.. --Michael Mol (talk) 20:59, 30 May 2020 (UTC)

# Earliest difference between prime gaps

Earliest difference between prime gaps is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

When calculating prime numbers > 2, the difference between adjacent primes is always an even number. This difference, also referred to as the gap, varies in an random pattern; at least, no pattern has ever been discovered, and it is strongly conjectured that no pattern exists. However, it is also conjectured that between some two adjacent primes will be a gap corresponding to every positive even integer.

gap minimal
starting
prime
ending
prime
2 3 5
4 7 11
6 23 29
8 89 97
10 139 149
12 199 211
14 113 127
16 1831 1847
18 523 541
20 887 907
22 1129 1151
24 1669 1693
26 2477 2503
28 2971 2999
30 4297 4327

This task involves locating the minimal primes corresponding to those gaps.

Though every gap value exists, they don't seem to come in any particular order. For example, this table shows the gaps and minimum starting value primes for 2 through 30:

For the purposes of this task, considering only primes greater than 2, consider prime gaps that differ by exactly two to be adjacent.

For each order of magnitude m from 10¹ through 10⁶:

• Find the first two sets of adjacent minimum prime gaps where where the absolute value of the difference between the prime gap start values is greater than m.

E.G.

For an m of 10¹;

The start value of gap 2 is 3, the start value of gap 4 is 7, the difference is 7 - 3 or 4. 4 < 10¹ so keep going.

The start value of gap 4 is 7, the start value of gap 6 is 23, the difference is 23 - 7, or 16. 16 > 10¹ so this the earliest adjacent gap difference > 10¹.

Stretch goal
• Do the same for 10⁷ and 10⁸ (and higher?) orders of magnitude

Note: the earliest value found for each order of magnitude may not be unique, in fact, is not unique; also, with the gaps in ascending order, the minimal starting values are not strictly ascending.

## C++

Library: Primesieve
`#include <iostream>#include <locale>#include <unordered_map> #include <primesieve.hpp> class prime_gaps {public:    prime_gaps() { last_prime_ = iterator_.next_prime(); }    uint64_t find_gap_start(uint64_t gap);private:    primesieve::iterator iterator_;    uint64_t last_prime_;    std::unordered_map<uint64_t, uint64_t> gap_starts_;}; uint64_t prime_gaps::find_gap_start(uint64_t gap) {    auto i = gap_starts_.find(gap);    if (i != gap_starts_.end())        return i->second;    for (;;) {        uint64_t prev = last_prime_;        last_prime_ = iterator_.next_prime();        uint64_t diff = last_prime_ - prev;        gap_starts_.emplace(diff, prev);        if (gap == diff)            return prev;    }} int main() {    std::cout.imbue(std::locale(""));    const uint64_t limit = 100000000000;    prime_gaps pg;    for (uint64_t pm = 10, gap1 = 2;;) {        uint64_t start1 = pg.find_gap_start(gap1);        uint64_t gap2 = gap1 + 2;        uint64_t start2 = pg.find_gap_start(gap2);        uint64_t diff = start2 > start1 ? start2 - start1 : start1 - start2;        if (diff > pm) {            std::cout << "Earliest difference > " << pm                      << " between adjacent prime gap starting primes:\n"                      << "Gap " << gap1 << " starts at " << start1 << ", gap "                      << gap2 << " starts at " << start2 << ", difference is "                      << diff << ".\n\n";            if (pm == limit)                break;            pm *= 10;        } else {            gap1 = gap2;        }    }}`
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16.

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 1,000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 10,000 between adjacent prime gap starting primes:
Gap 36 starts at 9,551, gap 38 starts at 30,593, difference is 21,042.

Earliest difference > 100,000 between adjacent prime gap starting primes:
Gap 70 starts at 173,359, gap 72 starts at 31,397, difference is 141,962.

Earliest difference > 1,000,000 between adjacent prime gap starting primes:
Gap 100 starts at 396,733, gap 102 starts at 1,444,309, difference is 1,047,576.

Earliest difference > 10,000,000 between adjacent prime gap starting primes:
Gap 148 starts at 2,010,733, gap 150 starts at 13,626,257, difference is 11,615,524.

Earliest difference > 100,000,000 between adjacent prime gap starting primes:
Gap 198 starts at 46,006,769, gap 200 starts at 378,043,979, difference is 332,037,210.

Earliest difference > 1,000,000,000 between adjacent prime gap starting primes:
Gap 276 starts at 649,580,171, gap 278 starts at 4,260,928,601, difference is 3,611,348,430.

Earliest difference > 10,000,000,000 between adjacent prime gap starting primes:
Gap 332 starts at 5,893,180,121, gap 334 starts at 30,827,138,509, difference is 24,933,958,388.

Earliest difference > 100,000,000,000 between adjacent prime gap starting primes:
Gap 386 starts at 35,238,645,587, gap 388 starts at 156,798,792,223, difference is 121,560,146,636.

```

## F#

This task uses Extensible Prime Generator (F#)

` // Earliest difference between prime gaps. Nigel Galloway: December 1st., 2021let fN y=let i=System.Collections.Generic.SortedDictionary<int64,int64>()         let fN()=i|>Seq.pairwise|>Seq.takeWhile(fun(n,g)->g.Key=n.Key+2L)|>Seq.tryFind(fun(n,g)->abs(n.Value-g.Value)>y)         (fun(n,g)->let e=g-n in match i.TryGetValue(e) with (false,_)->i.Add(e,n); fN() |_->None)[1..9]|>List.iter(fun g->let fN=fN(pown 10 g) in let n,i=(primes64()|>Seq.skip 1|>Seq.pairwise|>Seq.map fN|>Seq.find Option.isSome).Value                         printfn \$"%10d{pown 10 g} -> distance between start of gap %d{n.Key}=%d{n.Value} and start of gap %d{i.Key}=%d{i.Value} is %d{abs((n.Value)-(i.Value))}") `
Output:
```        10 -> distance between start of gap 4=7 and start of gap 6=23 is 16
100 -> distance between start of gap 14=113 and start of gap 16=1831 is 1718
1000 -> distance between start of gap 14=113 and start of gap 16=1831 is 1718
10000 -> distance between start of gap 36=9551 and start of gap 38=30593 is 21042
100000 -> distance between start of gap 70=173359 and start of gap 72=31397 is 141962
1000000 -> distance between start of gap 100=396733 and start of gap 102=1444309 is 1047576
10000000 -> distance between start of gap 148=2010733 and start of gap 150=13626257 is 11615524
100000000 -> distance between start of gap 198=46006769 and start of gap 200=378043979 is 332037210
1000000000 -> distance between start of gap 276=649580171 and start of gap 278=4260928601 is 3611348430
```

## Java

Uses the PrimeGenerator class from Extensible prime generator#Java.

`import java.util.HashMap;import java.util.Map; public class PrimeGaps {    private Map<Integer, Integer> gapStarts = new HashMap<>();    private int lastPrime;    private PrimeGenerator primeGenerator = new PrimeGenerator(1000, 500000);     public static void main(String[] args) {        final int limit = 100000000;        PrimeGaps pg = new PrimeGaps();        for (int pm = 10, gap1 = 2;;) {            int start1 = pg.findGapStart(gap1);            int gap2 = gap1 + 2;            int start2 = pg.findGapStart(gap2);            int diff = start2 > start1 ? start2 - start1 : start1 - start2;            if (diff > pm) {                System.out.printf(                    "Earliest difference > %,d between adjacent prime gap starting primes:\n"                    + "Gap %,d starts at %,d, gap %,d starts at %,d, difference is %,d.\n\n",                    pm, gap1, start1, gap2, start2, diff);                if (pm == limit)                    break;                pm *= 10;            } else {                gap1 = gap2;            }        }    }     private int findGapStart(int gap) {        Integer start = gapStarts.get(gap);        if (start != null)            return start;        for (;;) {            int prev = lastPrime;            lastPrime = primeGenerator.nextPrime();            int diff = lastPrime - prev;            gapStarts.putIfAbsent(diff, prev);            if (diff == gap)                return prev;        }    }}`
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16.

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 1,000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 10,000 between adjacent prime gap starting primes:
Gap 36 starts at 9,551, gap 38 starts at 30,593, difference is 21,042.

Earliest difference > 100,000 between adjacent prime gap starting primes:
Gap 70 starts at 173,359, gap 72 starts at 31,397, difference is 141,962.

Earliest difference > 1,000,000 between adjacent prime gap starting primes:
Gap 100 starts at 396,733, gap 102 starts at 1,444,309, difference is 1,047,576.

Earliest difference > 10,000,000 between adjacent prime gap starting primes:
Gap 148 starts at 2,010,733, gap 150 starts at 13,626,257, difference is 11,615,524.

Earliest difference > 100,000,000 between adjacent prime gap starting primes:
Gap 198 starts at 46,006,769, gap 200 starts at 378,043,979, difference is 332,037,210.

```

## Julia

Translation of: Wren

To get to 10^9 correctly we need a limit multiplier of 5 in Julia, not 4. Going up to 10^10 runs out of memory on my machine.

`using Formattingusing Primes function primegaps(limit = 10^9)    c(n) = format(n, commas=true)    pri = primes(limit * 5)    gapstarts = Dict{Int, Int}()    for i in 2:length(pri)        get!(gapstarts, pri[i] - pri[i - 1], pri[i - 1])    end    pm, gap1 = 10, 2    while true        while !haskey(gapstarts, gap1)            gap1 += 2        end        start1 = gapstarts[gap1]        gap2 = gap1 + 2        if !haskey(gapstarts, gap2)            gap1 = gap2 + 2            continue        end        start2 = gapstarts[gap2]        if ((diff = abs(start2 - start1)) > pm)            println("Earliest difference > \$(c(pm)) between adjacent prime gap starting primes:")            println("Gap \$gap1 starts at \$(c(start1)), gap \$(c(gap2)) starts at \$(c(start2)), difference is \$(c(diff)).\n")            pm == limit && break            pm *= 10        else            gap1 = gap2        end    endend primegaps() `
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16.

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 1,000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 10,000 between adjacent prime gap starting primes:
Gap 36 starts at 9,551, gap 38 starts at 30,593, difference is 21,042.

Earliest difference > 100,000 between adjacent prime gap starting primes:
Gap 70 starts at 173,359, gap 72 starts at 31,397, difference is 141,962.

Earliest difference > 1,000,000 between adjacent prime gap starting primes:
Gap 100 starts at 396,733, gap 102 starts at 1,444,309, difference is 1,047,576.

Earliest difference > 10,000,000 between adjacent prime gap starting primes:
Gap 148 starts at 2,010,733, gap 150 starts at 13,626,257, difference is 11,615,524.

Earliest difference > 100,000,000 between adjacent prime gap starting primes:
Gap 198 starts at 46,006,769, gap 200 starts at 378,043,979, difference is 332,037,210.

Earliest difference > 1,000,000,000 between adjacent prime gap starting primes:
Gap 276 starts at 649,580,171, gap 278 starts at 4,260,928,601, difference is 3,611,348,430.
```

## Pascal

### Free Pascal

`program primesieve;// sieving small ranges of 65536//{\$O+,R+}{\$IFDEF FPC}  {\$MODE DELPHI}{\$OPTIMIZATION ON,ALL}{\$CODEALIGN proc=32}  uses    sysutils;{\$ENDIF}{\$IFDEF WINDOWS}  {\$APPTYPE CONSOLE}{\$ENDIF} const  smlPrimes :array [0..10] of Byte = (2,3,5,7,11,13,17,19,23,29,31);  maxPreSievePrime = 17;  sieveSize = 1 shl 15;//32768*2 ->max count of FoundPrimes = 6542type  tSievePrim = record                 svdeltaPrime:word;//diff between actual and new prime                 svSivOfs:word;//-> sieveSize< 1 shl 16                 svSivNum:LongWord;// 1 shl (16+32) = 2.8e14               end;var{\$Align 16}  //primes up to 1E6-> sieving to 1E12  sievePrimes : array[0..78497] of tSievePrim;{\$Align 16}  preSieve :array[0..3*5*7*11*13*17-1] of Byte;{\$Align 16}  Sieve :array[0..sieveSize-1] of Byte;{\$Align 16}  FoundPrimes : array[0..6542] of LongWord;{\$Align 16}  Gaps  : array[0..255] Of Uint64;{\$Align 16}  Limit,OffSet : Uint64;   SieveMaxIdx,  preSieveOffset,  SieveNum,  FoundPrimesCnt,  PrimPos,  LastInsertedSievePrime :NativeUInt; procedure CopyPreSieveInSieve;forward;procedure CollectPrimes;forward;procedure sieveOneSieve;forward; procedure preSieveInit;var  i,pr,j,umf : NativeInt;Begin  fillchar(preSieve,SizeOf(preSieve),#1);  i := 1;// starts with pr = 3  umf := 1;  repeat    IF preSieve[i] <> 0 then    Begin      pr := 2*i+1;      j := i;      repeat        preSieve[j] := 0;        inc(j,pr);      until j> High(preSieve);      umf := umf*pr;    end;    inc(i);  until umf>High(preSieve);  preSieveOffset := 0;end; procedure CalcSievePrimOfs(lmt:NativeUint);var  i,pr : NativeUInt;  sq : Uint64;begin  pr := 0;  i := 0;  repeat    with sievePrimes[i] do    Begin      pr := pr+svdeltaPrime;      IF sqr(pr)  < (SieveSize*2) then      Begin        svSivNum := 0;        svSivOfs := (pr*pr-1) DIV 2;      end      else      Begin        SieveMaxIdx := i;        pr := pr-svdeltaPrime;        BREAK;      end;    end;    inc(i);  until i > lmt;   for i := i to lmt do  begin    with sievePrimes[i] do    Begin      pr := pr+svdeltaPrime;      sq := sqr(pr);      svSivNum := sq DIV (2*SieveSize);      svSivOfs := ( (sq - Uint64(svSivNum)*(2*SieveSize))-1)DIV 2;    end;  end;end; procedure InitSieve;begin  preSieveOffset := 0;  SieveNum :=0;  CalcSievePrimOfs(PrimPos-1);end; procedure InsertSievePrimes;var  j    :NativeUINt;  i,pr : NativeUInt;begin  i := 0;  //ignore first primes already sieved with  if SieveNum = 0 then    repeat      inc(i);    until FoundPrimes[i] > maxPreSievePrime;   pr :=0;  j := Uint64(SieveNum)*SieveSize*2-LastInsertedSievePrime;  with sievePrimes[PrimPos] do  Begin    pr := FoundPrimes[i];    svdeltaPrime := pr+j;    j := pr;    end;  inc(PrimPos);  for i := i+1 to FoundPrimesCnt-1 do  Begin    IF PrimPos > High(sievePrimes) then      BREAK;    with sievePrimes[PrimPos] do    Begin      pr := FoundPrimes[i];      svdeltaPrime := (pr-j);      j := pr;    end;    inc(PrimPos);  end;  LastInsertedSievePrime :=Uint64(SieveNum)*(SieveSize*2)+pr;end; procedure sievePrimesInit;var  i,j,pr:NativeInt;Begin  LastInsertedSievePrime := 0;   PrimPos := 0;  preSieveOffset := 0;  SieveNum :=0;  CopyPreSieveInSieve;  i := 1; // start with 3  repeat    while Sieve[i] = 0 do      inc(i);    pr := 2*i+1;    inc(i);    j := ((pr*pr)-1) DIV 2;    if j > High(Sieve) then      BREAK;    repeat      Sieve[j] := 0;      inc(j,pr);    until j > High(Sieve);  until false;   CollectPrimes;  InsertSievePrimes;  IF PrimPos < High(sievePrimes) then  Begin    InitSieve;    //Erste Sieb nochmals, aber ohne Eintrag    CopyPreSieveInSieve;    sieveOneSieve;    repeat      inc(SieveNum);      CopyPreSieveInSieve;      sieveOneSieve;      CollectPrimes;      InsertSievePrimes;   until PrimPos > High(sievePrimes);  end;end; procedure OutGaps(g1,g2,delta:NativeUint);begin  if g2= 0  then    writeln(2*g1:4,2*g1+2:4,delta:13,Gaps[g1]:13,Gaps[g1+1]:13)  else   writeln(2*g2-1:4,2*g1:4,delta:13,Gaps[g1-1]:13,Gaps[g1]:13);end;function GetDiffval(val1,val2: NativeInt): NativeInt;begin  if val1*val2 = 0 then    EXIT(0);  dec(val1,val2);  if val1<0 then    val1 :=-val1;  GetDiffval := val1;end; procedure CheckGaps;var  val1,val2,val3,i,DekaLimit : NativeInt;Begin  writeln('Gap1 Gap2   difference       first       second  prime');  dekaLimit := 10;  i := 1;  repeat    val1 := Gaps[i];    if val1 <> 0 then    Begin      val2 := GetDiffval(val1,Gaps[i-1]);      val3 := GetDiffval(val1,Gaps[i+1]);      while (val2>DekaLimit) or (val3>DekaLimit) do      begin        writeln(DekaLimit:21,'<');        if val2 = 0 then        begin          if val3 > 0 then            OutGaps(i,0,val3);        end        else        begin          if val3 = 0 then            OutGaps(i,1,val2)          else          Begin            if val3 > val2 then              OutGaps(i,0,val3)            else              OutGaps(i,1,val2);          end;        end;        DekaLimit := 10*DekaLimit;      end;    end;    inc(i);  until i>=254;end; procedure CopyPreSieveInSieve;var  lmt : NativeInt;Begin  lmt := preSieveOffset+sieveSize;  lmt := lmt-(High(preSieve)+1);  IF lmt<= 0 then  begin    Move(preSieve[preSieveOffset],Sieve,sieveSize);    if lmt <> 0 then      inc(preSieveOffset,sieveSize)    else      preSieveOffset := 0;  end  else  begin    Move(preSieve[preSieveOffset],Sieve,sieveSize-lmt);    Move(preSieve,Sieve[sieveSize-lmt],lmt);    preSieveOffset := lmt  end;end; procedure CollectPrimes;var   pSieve : pbyte;   pFound : pLongWord;   i,idx : NativeInt;Begin  pFound := @FoundPrimes;  idx := 0;  i := 0;  IF SieveNum = 0 then  Begin    repeat      pFound[idx] := smlPrimes[idx];      inc(idx);    until smlPrimes[idx]>maxPreSievePrime;    i := (smlPrimes[idx] -1) DIV 2;  end;   pSieve := @Sieve;  repeat    pFound[idx]:= 2*i+1;    inc(idx,pSieve[i]);    inc(i);  until i>High(Sieve);  FoundPrimesCnt:= idx;end; procedure sieveOneSieve;var  i,j,pr,dSievNum :NativeUint;Begin  pr := 0;  For i := 0 to SieveMaxIdx do    with sievePrimes[i] do    begin      pr := pr+svdeltaPrime;      IF svSivNum = sieveNum then      Begin        j := svSivOfs;        repeat          Sieve[j] := 0;          inc(j,pr);        until j > High(Sieve);         dSievNum := j DIV SieveSize;        svSivOfs := j-dSievNum*SieveSize;        inc(svSivNum,dSievNum);      end;    end;   i := SieveMaxIdx+1;  repeat    if i > High(SievePrimes) then      BREAK;    with sievePrimes[i] do    begin      if svSivNum > sieveNum then      Begin        SieveMaxIdx := I-1;        Break;      end;      pr := pr+svdeltaPrime;      j := svSivOfs;      repeat        Sieve[j] := 0;        inc(j,pr);      until j > High(Sieve);      dSievNum := j DIV SieveSize;      svSivOfs := j-dSievNum*SieveSize;      inc(svSivNum,dSievNum);      inc(i);    end;  until false;end; var  T1,T0,CNT,ActPrime,LastPrime,delta : Int64;  i: Int32; begin  T0 := GetTickCount64;  Limit := 10*1000*1000*1000;//158*1000*1000*1000;  preSieveInit;  sievePrimesInit;   InitSieve;  offset := 0;  Cnt := 1;//==2  LastPrime := 2;    repeat    CopyPreSieveInSieve;sieveOneSieve;CollectPrimes;    inc(Cnt,FoundPrimesCnt);    //collect first occurrence of gap    i := 0;    repeat      ActPrime := Offset+FoundPrimes[i];      delta := (ActPrime - LastPrime) shr 1;      If Gaps[delta] = 0 then        Gaps[delta] := LastPrime;      LastPrime := ActPrime;      inc(i);    until (i >= FoundPrimesCnt);     inc(SieveNum);    inc(offset,2*SieveSize);  until SieveNum > (Limit DIV (2*SieveSize));  CheckGaps;  T1 := GetTickCount64;  OffSet := Uint64(SieveNum-1)*(2*SieveSize);    i := FoundPrimesCnt;  repeat    dec(i);    dec(cnt);  until (i = 0) OR (OffSet+FoundPrimes[i]<Limit);  writeln;  writeln(cnt,' in ',Limit,' takes ',T1-T0,' ms');  {\$IFDEF WINDOWS}  writeln('Press <Enter>');readln;  {\$ENDIF}end.`
@TIO.RUN:
```Gap1 Gap2   difference       first       second  prime
10<
4   6           16            7           23
100<
14  16         1718          113         1831
1000<
14  16         1718          113         1831
10000<
36  38        21042         9551        30593
100000<
70  72       141962       173359        31397
1000000<
100 102      1047576       396733      1444309
10000000<
148 150     11615524      2010733     13626257
100000000<
198 200    332037210     46006769    378043979

50847534 in 1000000000 takes 886 ms
//@home primes til 158,000,000,000 like C++
276 278   3611348430    649580171   4260928601
10000000000<
332 334  24933958388   5893180121  30827138509
100000000000<
386 388 121560146636  35238645587 156798792223

6385991032 in 158000000000 takes 247532 ms
```

## Perl

`#!/usr/bin/perl use strict; # https://rosettacode.org/wiki/Earliest_difference_between_prime_gapsuse warnings;use ntheory qw( primes ); my @gaps;my \$primeref = primes( 1e9 );for my \$i ( 2 .. \$#\$primeref )  {  my \$diff = \$primeref->[\$i] - \$primeref->[\$i - 1];  \$gaps[ \$diff >> 1 ] //= \$primeref->[\$i - 1];  }my %first;for my \$i ( 1 .. \$#gaps )  {  defined \$gaps[\$i] && defined \$gaps[\$i-1] or next;  my \$diff = abs \$gaps[\$i] - \$gaps[\$i-1];  for my \$m ( map 10 ** \$_, 1 .. 10 )    {    \$diff > \$m and !\$first{\$m}++ and      print "above \$m gap @{[\$i * 2 - 2 ]} abs( \$gaps[\$i-1] - \$gaps[\$i] )\n";    }  }`
Output:
```above 10 gap 4 abs( 7 - 23 )
above 100 gap 14 abs( 113 - 1831 )
above 1000 gap 14 abs( 113 - 1831 )
above 10000 gap 36 abs( 9551 - 30593 )
above 100000 gap 70 abs( 173359 - 31397 )
above 1000000 gap 100 abs( 396733 - 1444309 )
above 10000000 gap 148 abs( 2010733 - 13626257 )
above 100000000 gap 198 abs( 46006769 - 378043979 )
```

## Phix

Translation of: Wren
```with javascript_semantics
constant limit = iff(platform()=JS?1e7:1e8),
gslim = 250
sequence primes = get_primes_le(limit*4),
gapstarts = repeat(0,gslim)
for i=2 to length(primes) do
integer gap = primes[i]-primes[i-1]
if gapstarts[gap]=0 then
gapstarts[gap] = primes[i-1]
end if
end for

integer pm = 10, gap1 = 2
while true do
while gapstarts[gap1]=0 do gap1 += 2 end while
integer start1 = gapstarts[gap1],
gap2 = gap1 + 2
if gapstarts[gap2]=0 then
gap1 = gap2 + 2
else
integer start2 = gapstarts[gap2],
diff = abs(start2 - start1)
if diff>pm then
printf(1,"Earliest difference >%,d between adjacent prime gap starting primes:\n",{pm})
printf(1,"Gap %d starts at %,d, gap %d starts at %,d, difference is %,d.\n\n",
{gap1,        start1,  gap2,        start2,            diff})
if pm=limit then exit end if
pm *= 10
else
gap1 = gap2
end if
end if
end while
```

Output same as Wren. Takes 5s on desktop/Phix but would take 17s under p2js so limited that to keep it under 2s. A limit of 1e9 needs 64 bit (hence not p2js compatible), and a multiplier of 5, and a gslim of 354, and takes 2 mins 43s, and nearly killed my poor little box, but matched the output of Julia, which managed it in 40s (and with no signs of any stress). Python needed more memory than I've got for 1e9, but took 15s for a limit of 1e8, while Wren (bless, also 1e8) took just over 3 minutes (an old i5/8GB/w10).

## Python

Translation of: Julia, Wren
`""" https://rosettacode.org/wiki/Earliest_difference_between_prime_gaps """ from primesieve import primes LIMIT = 10**9pri = primes(LIMIT * 5)gapstarts = {}for i in range(1, len(pri)):    if pri[i] - pri[i - 1] not in gapstarts:        gapstarts[pri[i] - pri[i - 1]] = pri[i - 1] PM, GAP1, = 10, 2while True:    while GAP1 not in gapstarts:        GAP1 += 2    start1 = gapstarts[GAP1]    GAP2 = GAP1 + 2    if GAP2 not in gapstarts:        GAP1 = GAP2 + 2        continue    start2 = gapstarts[GAP2]    diff = abs(start2 - start1)    if diff > PM:        print(f"Earliest difference >{PM: ,} between adjacent prime gap starting primes:")        print(f"Gap {GAP1} starts at{start1: ,}, gap {GAP2} starts at{start2: ,}, difference is{diff: ,}.\n")        if PM == LIMIT:            break        PM *= 10    else:        GAP1 = GAP2 `
Output:
Same as Raku, Wren and Julia versions.

## Raku

1e1 through 1e7 are pretty speedy (less than 5 seconds total). 1e8 and 1e9 take several minutes.

`use Math::Primesieve;use Lingua::EN::Numbers; my \$iterator = Math::Primesieve::iterator.new;my @gaps;my \$last = 2; for 1..9 {    my \$m = exp \$_, 10;    my \$this;    loop {        \$this = (my \$p = \$iterator.next) - \$last;        if !@gaps[\$this].defined {             @gaps[\$this]= \$last;             check-gap(\$m, \$this, @gaps) && last               if \$this > 2 and @gaps[\$this - 2].defined and (abs(\$last - @gaps[\$this - 2]) > \$m);        }        \$last = \$p;    }} sub check-gap (\$n, \$this, @p) {    my %upto = @p[^\$this].pairs.grep: *.value;    my @upto = (1..\$this).map: { last unless %upto{\$_ * 2}; %upto{\$_ * 2} }    my \$key = @upto.rotor(2=>-1).first( {.sink; abs(. - .) > \$n}, :k );    return False unless \$key;    say "Earliest difference > {comma \$n} between adjacent prime gap starting primes:";    printf "Gap %s starts at %s, gap %s starts at %s, difference is %s\n\n",    |(2 * \$key + 2, @upto[\$key], 2 * \$key + 4, @upto[\$key+1], abs(@upto[\$key] - @upto[\$key+1]))».&comma;    True}`
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718

Earliest difference > 1,000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718

Earliest difference > 10,000 between adjacent prime gap starting primes:
Gap 36 starts at 9,551, gap 38 starts at 30,593, difference is 21,042

Earliest difference > 100,000 between adjacent prime gap starting primes:
Gap 70 starts at 173,359, gap 72 starts at 31,397, difference is 141,962

Earliest difference > 1,000,000 between adjacent prime gap starting primes:
Gap 100 starts at 396,733, gap 102 starts at 1,444,309, difference is 1,047,576

Earliest difference > 10,000,000 between adjacent prime gap starting primes:
Gap 148 starts at 2,010,733, gap 150 starts at 13,626,257, difference is 11,615,524

Earliest difference > 100,000,000 between adjacent prime gap starting primes:
Gap 198 starts at 46,006,769, gap 200 starts at 378,043,979, difference is 332,037,210

Earliest difference > 1,000,000,000 between adjacent prime gap starting primes:
Gap 276 starts at 649,580,171, gap 278 starts at 4,260,928,601, difference is 3,611,348,430```

## Rust

`// [dependencies]// primal = "0.3" fn main() {    use std::collections::HashMap;     let mut primes = primal::Primes::all();    let mut last_prime = primes.next().unwrap();    let mut gap_starts = HashMap::new();     let mut find_gap_start = move |gap: usize| -> usize {        if let Some(start) = gap_starts.get(&gap) {            return *start;        }        loop {            let prev = last_prime;            last_prime = primes.next().unwrap();            let diff = last_prime - prev;            if !gap_starts.contains_key(&diff) {                gap_starts.insert(diff, prev);            }            if gap == diff {                return prev;            }        }    };     let limit = 100000000000;     let mut pm = 10;    let mut gap1 = 2;    loop {        let start1 = find_gap_start(gap1);        let gap2 = gap1 + 2;        let start2 = find_gap_start(gap2);        let diff = if start2 > start1 {            start2 - start1        } else {            start1 - start2        };        if diff > pm {            println!(                "Earliest difference > {} between adjacent prime gap starting primes:\n\                Gap {} starts at {}, gap {} starts at {}, difference is {}.\n",                pm, gap1, start1, gap2, start2, diff            );            if pm == limit {                break;            }            pm *= 10;        } else {            gap1 = gap2;        }    }}`
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16.

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1831, difference is 1718.

Earliest difference > 1000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1831, difference is 1718.

Earliest difference > 10000 between adjacent prime gap starting primes:
Gap 36 starts at 9551, gap 38 starts at 30593, difference is 21042.

Earliest difference > 100000 between adjacent prime gap starting primes:
Gap 70 starts at 173359, gap 72 starts at 31397, difference is 141962.

Earliest difference > 1000000 between adjacent prime gap starting primes:
Gap 100 starts at 396733, gap 102 starts at 1444309, difference is 1047576.

Earliest difference > 10000000 between adjacent prime gap starting primes:
Gap 148 starts at 2010733, gap 150 starts at 13626257, difference is 11615524.

Earliest difference > 100000000 between adjacent prime gap starting primes:
Gap 198 starts at 46006769, gap 200 starts at 378043979, difference is 332037210.

Earliest difference > 1000000000 between adjacent prime gap starting primes:
Gap 276 starts at 649580171, gap 278 starts at 4260928601, difference is 3611348430.

Earliest difference > 10000000000 between adjacent prime gap starting primes:
Gap 332 starts at 5893180121, gap 334 starts at 30827138509, difference is 24933958388.

Earliest difference > 100000000000 between adjacent prime gap starting primes:
Gap 386 starts at 35238645587, gap 388 starts at 156798792223, difference is 121560146636.

```

## Wren

Library: Wren-math
Library: Wren-fmt

This uses a segmented sieve to avoid running out of memory when looking for the earliest difference above 1 billion. Takes a little over 5½ minutes to run (25 seconds to reach first 100 million) on my machine (core i7, 32GB RAM, Ubuntu 20.04).

`import "./math" for Intimport "/fmt" for Fmt var limit = 1e9var gapStarts = {}var primes = Int.segmentedSieve(limit * 5, 8 * 1024 * 1024) // 8 MB cachefor (i in 1...primes.count) {    var gap = primes[i] - primes[i-1]    if (!gapStarts[gap]) gapStarts[gap] = primes[i-1]}var pm = 10var gap1 = 2while (true) {    while (!gapStarts[gap1]) gap1 = gap1 + 2    var start1 = gapStarts[gap1]    var gap2 = gap1 + 2    if (!gapStarts[gap2]) {        gap1 = gap2 + 2        continue    }    var start2 = gapStarts[gap2]    var diff = (start2 - start1).abs    if (diff > pm) {        Fmt.print("Earliest difference > \$,d between adjacent prime gap starting primes:", pm)        Fmt.print("Gap \$d starts at \$,d, gap \$d starts at \$,d, difference is \$,d.\n", gap1, start1, gap2, start2, diff)        if (pm == limit) break        pm = pm * 10    } else {        gap1 = gap2    }}`
Output:
```Earliest difference > 10 between adjacent prime gap starting primes:
Gap 4 starts at 7, gap 6 starts at 23, difference is 16.

Earliest difference > 100 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 1,000 between adjacent prime gap starting primes:
Gap 14 starts at 113, gap 16 starts at 1,831, difference is 1,718.

Earliest difference > 10,000 between adjacent prime gap starting primes:
Gap 36 starts at 9,551, gap 38 starts at 30,593, difference is 21,042.

Earliest difference > 100,000 between adjacent prime gap starting primes:
Gap 70 starts at 173,359, gap 72 starts at 31,397, difference is 141,962.

Earliest difference > 1,000,000 between adjacent prime gap starting primes:
Gap 100 starts at 396,733, gap 102 starts at 1,444,309, difference is 1,047,576.

Earliest difference > 10,000,000 between adjacent prime gap starting primes:
Gap 148 starts at 2,010,733, gap 150 starts at 13,626,257, difference is 11,615,524.

Earliest difference > 100,000,000 between adjacent prime gap starting primes:
Gap 198 starts at 46,006,769, gap 200 starts at 378,043,979, difference is 332,037,210.

Earliest difference > 1,000,000,000 between adjacent prime gap starting primes:
Gap 276 starts at 649,580,171, gap 278 starts at 4,260,928,601, difference is 3,611,348,430.
```