OFFSET
1,1
COMMENTS
a(31) > 2*10^5. - Robert Price, Nov 14 2013
EXAMPLE
3^3 - 20 = 7 (prime), so 3 is in the sequence.
MATHEMATICA
Do[If[PrimeQ[3^n - 20], Print[n]], {n, 3, 10000}]
PROG
(PARI) is(n)=isprime(3^n-20) \\ Charles R Greathouse IV, Feb 17 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Nicolas M. Perrault, Nov 10 2012
EXTENSIONS
a(27)-a(30) from Robert Price, Nov 14 2013
STATUS
approved