OFFSET
1,2
COMMENTS
For s = 5,8,11,14,17,20,..., n_s=1+n+n^s is always composite for any n>1. Also at n=1, n_s=3 is a prime for any s. So it is interesting to consider only the cases of s =/= 5,8,11,14,17,20,... and n>1. Here i consider the case s=18 and find several first n's making n_s a prime (or a probable prime).
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1500
EXAMPLE
2 is OK because at s=18, n=2, n_s=1+n+n^s=262147 is a prime.
MATHEMATICA
Select[Range[1800], PrimeQ[1 + # + #^18] &] (* Harvey P. Dale, Mar 24 2011 *)
PROG
(PARI) for(n=1, 1000, if(isprime(1+n+n^18), print1(n", ")))
(Magma) [n: n in [0..1600] | IsPrime(s) where s is 1+n+n^18]; // Vincenzo Librandi, Jul 28 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Oct 03 2002
EXTENSIONS
More terms from Ralf Stephan, Apr 05 2003
STATUS
approved