A133378 a(1)=1. For n >= 2, a(n) = the largest prime divisor of (a(n-1)^a(n-1) + 1).

1, 2, 5, 521

Offset

1,2

Comments

a(5) depends on the factorization of the 1379-digit composite number; see factordb.com link. - Michael S. Branicky, Jan 27 2023; updated by Max Alekseyev, Jun 30 2026

Links

Table of n, a(n) for n=1..4.

factordb.com, 521^521+1.

Mathematica

NestList[FactorInteger[#^#+1][[-1, 1]]&, 1, 3] (* Harvey P. Dale, Jun 21 2012 *)

Crossrefs

Cf. A007571.

Sequence in context: A138696 A163798 A081296 * A283561 A037063 A068105

Adjacent sequences: A133375 A133376 A133377 * A133379 A133380 A133381

Keyword

more,nonn,changed

Author

Leroy Quet, Oct 28 2007

Status

approved