OFFSET
1,3
COMMENTS
From Carl R. White, Oct 23 2010: (Start)
Entries where a(n) = 1 can be found in A014224.
Entries where a(n) = -1 can be found in A181484. (End)
EXAMPLE
3^1-2^0 = 2, so a(1)=0; no other terms are zero.
3^11-2^1, 3^11-2^2, 3^11-2^3 are all nonprime, but 3^11-2^4 = 177131 which is prime so a(11) = 4.
a(36) is -1 (the placeholder value) because nonprimes are obtained when any power of two is subtracted from 3^36.
CROSSREFS
KEYWORD
sign
AUTHOR
Carl R. White, Aug 25 2010
STATUS
approved