OFFSET
1,1
COMMENTS
If n == 5 mod 6 (A016969), k^n + k - 1 is always divisible by k^2 - k + 1. Thus it will never be prime.
MATHEMATICA
lnk[n_]:=Module[{k=2}, While[CompositeQ[k^n+k-1], k++]; k]; Table[If[Mod[n, 6] == 5, 0, lnk[n]], {n, 90}] (* Harvey P. Dale, Oct 24 2021 *)
PROG
(PARI) a(n)=if(n==Mod(5, 6), return(0)); k=1; while(!isprime(k^n+k-1), k++); k
vector(100, n, a(n))
CROSSREFS
KEYWORD
nonn
AUTHOR
Derek Orr, Sep 30 2014
STATUS
approved