OFFSET
1,1
EXAMPLE
2*(2^2-1)*(2^3-1)*(2^5-1) + 1 = 1303 is prime, so a(1) = 2.
MATHEMATICA
f[n_] := Module[{k = 1}, While[! PrimeQ[k*n + 1], k++]; k]; f /@ Times @@@ Partition[2^MersennePrimeExponent[Range[15]] - 1, 3, 1] (* Amiram Eldar, Jul 18 2021 *)
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Pierre CAMI, Oct 22 2004
EXTENSIONS
a(11) inserted and a(17)-a(24) added by Amiram Eldar, Jul 18 2021
STATUS
approved