A096225 a(0) = 1; for n >= 0, a(n+1) = smallest prime factor of a(n)! + 1.

1, 2, 3, 7, 71, 6653, 25469, 15750503

Offset

0,2

Links

Table of n, a(n) for n=0..7.

Example

71!+1 is the product of 6653 and a large prime.

Mathematica

a[1] = 2; a[n_] := Block[{p = PrimePi[a[n - 1]] + 1, r = a[n - 1]! + 1}, While[ Mod[r, Prime[p]] != 0, p++ ]; Prime[p]]; Do[ Print[ a[n]], {n, 7}] (* Robert G. Wilson v, Aug 12 2004 *)
NestList[FactorInteger[#!+1][[1, 1]]&, 1, 7] (* Harvey P. Dale, Sep 20 2016 *)

Crossrefs

Cf. A002583, A051301.

Sequence in context: A090870 A088542 A075840 * A333132 A035094 A084729

Adjacent sequences: A096222 A096223 A096224 * A096226 A096227 A096228

Keyword

nonn,more,hard,nice

Author

N. J. A. Sloane, Aug 09 2004

Extensions

a(6) and a(7) from Robert G. Wilson v, Aug 12 2004

Status

approved