OFFSET
1,2
EXAMPLE
2*((6*1)^1) + 1 = 13 prime, so a(1)=1
2*((6*2)^1) + 1 = 25 = 5^2
2*((6*2)^2) + 1 = 289 = 17^2
2*((6*2)^3) + 1 = 3457 prime, so a(2)=3
MATHEMATICA
lk[n_]:=Module[{k=1}, While[!PrimeQ[2(6n)^k+1], k++]; k]; Array[lk, 110] (* Harvey P. Dale, May 16 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Pierre CAMI, Oct 13 2004
EXTENSIONS
Extended by R. J. Mathar, Nov 13 2009
STATUS
approved