1,4

Indices of 1's: A002981.

Table of n, a(n) for n=1..77.

Table[k = 1; While[! PrimeQ[k!*n! + 1], k++]; k, {n, 100}] (* T. D. Noe, Nov 18 2013 *)

Cf. A002981, A035093, A057217, A075757, A075758, A231901.

Sequence in context: A040015 A144926 A153016 * A088610 A026185 A026209

Adjacent sequences: A231546 A231547 A231548 * A231550 A231551 A231552

nonn

Alex Ratushnyak, Nov 15 2013

approved