Quadrat special primes: Difference between revisions
Added Algol 68
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where '''n''' < '''16000'''.
<br><br>
=={{header|ALGOL 68}}==
{{Trans|ALGOL W}}
<lang algol68>BEGIN # find some primes where the gap between the current prime and the next is a square #
# reurns a sieve of primes up to n #
PROC eratosthenes = ( INT n )[]BOOL:
BEGIN
[ 1 : n ]BOOL p;
p[ 1 ] := FALSE; p[ 2 ] := TRUE;
FOR i FROM 3 BY 2 TO n DO p[ i ] := TRUE OD;
FOR i FROM 4 BY 2 TO n DO p[ i ] := FALSE OD;
FOR i FROM 3 BY 2 TO ENTIER sqrt( n ) DO
IF p[ i ] THEN FOR s FROM i * i BY i + i TO n DO p[ s ] := FALSE OD FI
OD;
p
END # eratosthenes # ;
# an array of squares #
PROC get squares = ( INT n )[]INT:
BEGIN
[ 1 : n ]INT s;
FOR i TO n DO s[ i ] := i * i OD;
s
END # get squares # ;
INT max number = 16000;
[]BOOL prime = eratosthenes( max number );
[]INT square = get squares( max number );
INT p count, this prime, next prime;
# the first square gap is 1 (between 2 and 3) the gap between all other primes is even #
# so we treat 2-3 as a special case #
p count := 1; this prime := 2; next prime := 3;
print( ( " ", whole( this prime, -5 ) ) );
WHILE next prime < max number DO
this prime := next prime;
p count +:= 1;
print( ( " ", whole( this prime, -5 ) ) );
IF p count MOD 12 = 0 THEN print( ( newline ) ) FI;
INT sq pos := 2;
WHILE next prime := this prime + square[ sq pos ];
IF next prime < max number THEN NOT prime[ next prime ] ELSE FALSE FI
DO sq pos +:= 2 OD
OD
END</lang>
{{out}}
<pre>
2 3 7 11 47 83 227 263 587 911 947 983
1019 1163 1307 1451 1487 1523 1559 2459 3359 4259 4583 5483
5519 5843 5879 6203 6779 7103 7247 7283 7607 7643 8219 8363
10667 11243 11279 11423 12323 12647 12791 13367 13691 14591 14627 14771
15671
</pre>
=={{header|ALGOL W}}==
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