OFFSET
1,1
COMMENTS
a(n) = 1 for nonzero n in A045751. - Michel Marcus, Aug 01 2015
LINKS
Paolo Xausa, Table of n, a(n) for n = 1..10000
EXAMPLE
a(7)=3 because 7*2^2 + 1 = 29 is prime and 7*2^(2^2) + 1 = 113 is also prime, while 7*2^(2^3) + 1 = 11*163.
MATHEMATICA
A260821[n_] := Module[{k = 0}, While[PrimeQ[n*2^(2^++k) + 1]]; k];
Array[A260821, 100] (* Paolo Xausa, Jan 31 2024 *)
PROG
(PARI) a(n) = {k = 1; while (isprime(n*2^2^k+1), k++); k; } \\ Michel Marcus, Aug 01 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Marco Ripà, Jul 31 2015
EXTENSIONS
More terms from Michel Marcus, Aug 01 2015
STATUS
approved