Prime triplets: Difference between revisions
Added Algol 68
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:* The RosettaCode task for just (p,p+4): [[Cousin primes]]
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=={{header|ALGOL 68}}==
Using code from [[Successive_prime_differences#ALGOL_68]]
<lang algol68>BEGIN # find primes p where p+2 and p+6 are also prime #
# reurns a list of primes up to n #
PROC prime list = ( INT n )[]INT:
BEGIN
# sieve the primes to n #
INT no = 0, yes = 1;
[ 1 : n ]INT p;
p[ 1 ] := no; p[ 2 ] := yes;
FOR i FROM 3 BY 2 TO n DO p[ i ] := yes OD;
FOR i FROM 4 BY 2 TO n DO p[ i ] := no OD;
FOR i FROM 3 BY 2 TO ENTIER sqrt( n ) DO
IF p[ i ] = yes THEN FOR s FROM i * i BY i + i TO n DO p[ s ] := no OD FI
OD;
# replace the sieve with a list #
INT p pos := 0;
FOR i TO n DO IF p[ i ] = yes THEN p[ p pos +:= 1 ] := i FI OD;
p[ 1 : p pos ]
END # prime list # ;
# prints the elements of list #
PROC print list = ( INT width, []INT list )VOID:
BEGIN
print( ( "[" ) );
FOR i FROM LWB list TO UPB list DO print( ( " ", whole( list[ i ], width ) ) ) OD;
print( ( " ]" ) )
END # print list # ;
# attempts to find patterns in the differences of primes and prints the results #
PROC try differences = ( []INT primes, []INT pattern )VOID:
BEGIN
INT pattern length = ( UPB pattern - LWB pattern ) + 1;
[ 1 : pattern length + 1 ]INT first; FOR i TO UPB first DO first[ i ] := 0 OD;
[ 1 : pattern length + 1 ]INT last; FOR i TO UPB last DO last[ i ] := 0 OD;
INT count := 0;
FOR p FROM LWB primes + pattern length TO UPB primes DO
BOOL matched := TRUE;
INT e pos := LWB pattern;
FOR e FROM p - pattern length TO p - 1
WHILE matched := primes[ e + 1 ] - primes[ e ] = pattern[ e pos ]
DO
e pos +:= 1
OD;
IF matched THEN
# found a matching sequence #
count +:= 1;
print list( -4, primes[ p - pattern length : p ] );
IF count MOD 6 = 0 THEN print( ( newline ) ) ELSE print( ( " " ) ) FI
FI
OD;
print( ( newline, "Found ", whole( count, 0 ), " prime sequence(s) that differ by: " ) );
print list( 0, pattern );
print( ( newline ) )
END # try differences # ;
INT max number = 5 500;
[]INT p list = prime list( max number - 1 );
print( ( "Prime triplets under ", whole( max number, 0 ), ":", newline ) );
try differences( p list, ( 2, 4 ) )
END</lang>
{{out}}
<pre>
Prime triplets under 5500:
[ 5 7 11 ] [ 11 13 17 ] [ 17 19 23 ] [ 41 43 47 ] [ 101 103 107 ] [ 107 109 113 ]
[ 191 193 197 ] [ 227 229 233 ] [ 311 313 317 ] [ 347 349 353 ] [ 461 463 467 ] [ 641 643 647 ]
[ 821 823 827 ] [ 857 859 863 ] [ 881 883 887 ] [ 1091 1093 1097 ] [ 1277 1279 1283 ] [ 1301 1303 1307 ]
[ 1427 1429 1433 ] [ 1481 1483 1487 ] [ 1487 1489 1493 ] [ 1607 1609 1613 ] [ 1871 1873 1877 ] [ 1997 1999 2003 ]
[ 2081 2083 2087 ] [ 2237 2239 2243 ] [ 2267 2269 2273 ] [ 2657 2659 2663 ] [ 2687 2689 2693 ] [ 3251 3253 3257 ]
[ 3461 3463 3467 ] [ 3527 3529 3533 ] [ 3671 3673 3677 ] [ 3917 3919 3923 ] [ 4001 4003 4007 ] [ 4127 4129 4133 ]
[ 4517 4519 4523 ] [ 4637 4639 4643 ] [ 4787 4789 4793 ] [ 4931 4933 4937 ] [ 4967 4969 4973 ] [ 5231 5233 5237 ]
[ 5477 5479 5483 ]
Found 43 prime sequence(s) that differ by: [ 2 4 ]
</pre>
=={{header|AWK}}==
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Prime Triplets 1-5499: 43
</pre>
=={{header|Fermat}}==
<lang fermat>for i=3,5499,2 do if Isprime(i)=1 and Isprime(i+2)=1 and Isprime(i+6)=1 then !!(i,i+2,i+6) fi od</lang>
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