Ultra useful primes: Difference between revisions
Added Algol 68
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* [[oeis:A058220|OEIS:A058220 - Ultra-useful primes: smallest k such that 2^(2^n) - k is prime]]
=={{header|ALGOL 68}}==
{{works with|ALGOL 68G|Any - tested with release 2.8.3.win32}}
Uses Algol 68G's LONG LONG INT which has programmer-specifiable precision. Uses Miller Rabin primality testing.
{{libheader|ALGOL 68-primes}}
<lang algol68>BEGIN # find members of the sequence a(n) = smallest k such that 2^(2^n) - k is prime #
PR precision 650 PR # set number of digits for LONG LOMG INT #
# 2^(2^10) has 308 digits but we need more for #
# Miller Rabin primality testing #
PR read "primes.incl.a68" PR # include the prime related utilities #
FOR n TO 10 DO
LONG LONG INT two up 2 up n = LONG LONG INT( 2 ) ^ ( 2 ^ n );
FOR i BY 2
WHILE BOOL found a prime = is probably prime( two up 2 up n - i );
IF found a prime THEN
# found a sequence member #
print( ( " ", whole( i, 0 ) ) );
FALSE # stop looking #
ELSE
TRUE # haven't found a sequence member yet #
FI
DO SKIP OD
OD
END</lang>
{{out}}
<pre>
1 3 5 15 5 59 159 189 569 105
</pre>
=={{header|Factor}}==
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