Cubic special primes: Difference between revisions
Added Algol W
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END</lang>
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2 3 11 19 83 1811 2027 2243 2251 2467 2531 2539 3539 3547 4547 5059 10891 12619 13619 13627 13691 13907 14419
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=={{header|ALGOL W}}==
<lang algolw>begin % find a sequence of primes where the members differ by a cube %
integer MAX_PRIME, MAX_CUBE;
MAX_PRIME := 15000;
MAX_CUBE := entier( exp( ln( MAX_PRIME ) / 3 ) );
begin
logical array prime ( 1 :: MAX_PRIME );
integer array cube ( 1 :: MAX_CUBE );
integer p, q, c;
% sieve the primes to MAX_PRIME %
prime( 1 ) := false; prime( 2 ) := true;
for i := 3 step 2 until MAX_PRIME do prime( i ) := true;
for i := 4 step 2 until MAX_PRIME do prime( i ) := false;
for i := 3 step 2 until entier( sqrt( MAX_PRIME ) ) do begin
integer ii; ii := i + i;
if prime( i ) then for s := i * i step ii until MAX_PRIME do prime( s ) := false
end for_i;
% construct a table of cubes, we will need at most the cube root of max prime %
for i := 1 until MAX_CUBE do cube( i ) := i * i * i;
% find the prime sequence %
writeon( "2" );
p := 2;
while p < MAX_PRIME do begin
% find a prime that is p + a cube %
c := 1;
q := p + cube( c );
while if q > MAX_PRIME then false else not prime( q ) do begin
c := c + 1;
q := p + cube( c )
end while_not_prime_q ;
if q <= MAX_PRIME then writeon( i_w := 1, s_w := 0, " ", q );
p := q
end while_p_lt_MAX_PRIME
end;
write()
end.</lang>
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