Mersenne primes: Difference between revisions

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=={{header|ALGOL 68}}==

{{works with|ALGOL 68G|Any - tested with release 2.8.3.win32}}

<syntaxhighlight lang="algol68">

BEGIN # find some Mersenne Primrs - primes of the form 2^n - 1, n must be prime #

# This assumes LONG INT is at least 64 bits (as in e.g. Algol 68G) #

# we handle 2 as a special case and then the odd numbers starting at 3 #

PR read "primes.incl.a68" PR # include prime utilities #

# 2^0 - 1 = 0 and 2^1 - 1 = 1, neither of which is prime #

# start from 2^2 #

INT n := 2;

LONG INT p2 := 4;

IF is probably prime( p2 - 1 ) THEN print( ( " ", whole( n, 0 ) ) ) FI;

# 2^3, 2^5, etc. #

n +:= 1;

p2 *:= 2;

WHILE n < 61 DO

IF is probably prime( p2 - 1 ) THEN print( ( " ", whole( n, 0 ) ) ) FI;

n +:= 2;

p2 *:= 4

OD;

IF is probably prime( p2 - 1 ) THEN print( ( " ", whole( n, 0 ) ) ) FI

END

</syntaxhighlight>

{{out}}

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2 3 5 7 13 17 19 31 61