OFFSET
0,10
LINKS
Pierre CAMI, Table of n, a(n) for n = 0..1600
EXAMPLE
3*2^0*(2^1-1)-1=2 is prime so a(0)=1;
3*2^1*(2^1-1)-1=5 is prime as well as 7 so a(1)=1;
3*2^2*(2^1-1)-1=23 is prime so a(2)=1.
PROG
(PARI) a(n) = my(k=1); while ((x=3*2^n*(2^k-1)) && !isprime(x-1) && !isprime(x+1), k++); k; \\ Michel Marcus, Sep 16 2019; corrected Jun 14 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Nov 26 2008
STATUS
approved