OFFSET
0,4
EXAMPLE
a(5)=4 because 2^5+1+4=37 that is a prime.
PROG
(PARI) a(n) = k = 0; while (! isprime(2^n+k+1), k++); k; \\ Michel Marcus, Sep 27 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from Erich Friedman
STATUS
approved