OFFSET
1,1
EXAMPLE
19 = 2*3^2 + 1; 52489 = 8*3^8 + 1; a(3) = 32*3^32 + 1; a(4) = 54*3^54 + 1.
MAPLE
#choose N large, then S is the desired set
f:=n->n*3^n + 1:
S:={}:
for n from 0 to N do if(isprime(f(n))) then S:=S union {f(n)}: fi: od
MATHEMATICA
Select[Table[n*3^n + 1, {n, 0, 580}], PrimeQ] (* Jayanta Basu, Jun 01 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Patrick Devlin, Apr 26 2012
STATUS
approved