Find adjacent primes which differ by a square integer: Difference between revisions
Find adjacent primes which differ by a square integer (view source)
Revision as of 08:27, 20 April 2023
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981887 - 981823 = 64 = 8^2
997877 - 997813 = 64 = 8^2</pre>
=={{header|Delphi}}==
{{works with|Delphi|6.0}}
{{libheader|SysUtils,StdCtrls}}
<syntaxhighlight lang="Delphi">
function IsPrime(N: integer): boolean;
{Optimised prime test - about 40% faster than the naive approach}
var I,Stop: integer;
begin
if (N = 2) or (N=3) then Result:=true
else if (n <= 1) or ((n mod 2) = 0) or ((n mod 3) = 0) then Result:= false
else
begin
I:=5;
Stop:=Trunc(sqrt(N));
Result:=False;
while I<=Stop do
begin
if ((N mod I) = 0) or ((N mod (i + 2)) = 0) then exit;
Inc(I,6);
end;
Result:=True;
end;
end;
function GetNextPrime(Start: integer): integer;
{Get the next prime number after Start}
begin
repeat Inc(Start)
until IsPrime(Start);
Result:=Start;
end;
procedure ShowPrimeDiffs(Memo: TMemo);
var P1,P2,D: integer;
begin
P1:=GetNextPrime(2);
repeat
begin
P2:=GetNextPrime(P1);
D:=P2 - P1;
if (D>36) and (Frac(sqrt(D))=0) then
begin
Memo.Lines.Add(IntToStr(P2)+' - '+IntToStr(P1)+' = '+IntToStr(D));
end;
P1:=P2;
end
until P2>=1000000;
end;
</syntaxhighlight>
{{out}}
<pre>
89753 - 89689 = 64
107441 - 107377 = 64
288647 - 288583 = 64
368021 - 367957 = 64
381167 - 381103 = 64
396833 - 396733 = 100
400823 - 400759 = 64
445427 - 445363 = 64
623171 - 623107 = 64
625763 - 625699 = 64
637067 - 637003 = 64
710777 - 710713 = 64
725273 - 725209 = 64
779477 - 779413 = 64
801947 - 801883 = 64
803813 - 803749 = 64
821741 - 821677 = 64
832583 - 832519 = 64
838349 - 838249 = 100
844841 - 844777 = 64
883871 - 883807 = 64
912167 - 912103 = 64
919511 - 919447 = 64
954827 - 954763 = 64
981887 - 981823 = 64
997877 - 997813 = 64
</pre>
=={{header|F_Sharp|F#}}==
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