Mersenne primes: Difference between revisions
Added Algol W
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2 ^ 19 - 1
2 ^ 31 - 1
</pre>
=={{header|ALGOL W}}==
<syntaxhighlight lang="algolw">
begin % find some Mersenne Primrs - primrs of the form 2^n - 1, n must be prime %
% integers are 32 bit in Algol W, so there won't be many numbers to check %
% we handle 2 as a special case and then the odd numbers starting at 3 %
% simplified primality by trial division test - no need to check for even %
% numbers as 2^n - 1 is always odd for n >= 2 %
logical procedure oddOnlyPrimalityTest ( integer value n ) ;
begin
logical isPrime;
isPrime := true;
for i := 3 step 2 until entier( sqrt( n ) ) do begin;
isPrime := n rem i not = 0;
if not isPrime then goto endPrimalityTest
end for_i;
endPrimalityTest: isPrime
end oddOnlyPrimalityTest ;
integer p2, n;
n := 2;
p2 := 4;
if oddOnlyPrimalityTest( p2 - 1 ) then writeon( i_w := 1, s_w := 0, " ", n );
n := n + 1;
p2 := p2 * 2;
while n <= 31 do begin
if oddOnlyPrimalityTest( p2 - 1 ) then writeon( i_w := 1, s_w := 0, " ", n );
n := n + 2;
p2 := p2 * 4
end while_n_le_31
end.
</syntaxhighlight>
{{out}}
<pre>
2 3 5 7 13 17 19 31
</pre>
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