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=7 and find several first n's making n_s a prime (or a probable prime).
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
EXAMPLE
15 is OK because at s=7, n=15, n_s = 1 + n + n^s = 170859391 is a prime.
MATHEMATICA
Select[Range[1000], PrimeQ[1 + # + #^7] &] (* Vincenzo Librandi, Jul 28 2014 *)
PROG
(Magma) [n: n in [0..1000] | IsPrime(s) where s is 1+n+n^7]; // Vincenzo Librandi, Jul 28 2014
(PARI) for(n=1, 10^3, if(isprime(n^7+n+1), print1(n, ", "))) \\ Derek Orr, Feb 07 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Oct 03 2002
EXTENSIONS
More terms from Ralf Stephan, Apr 05 2003
STATUS
approved