A364820 a(n) is the smallest prime factor of the n-th Pell number A000129(n).

2, 5, 2, 29, 2, 13, 2, 5, 2, 5741, 2, 33461, 2, 5, 2, 137, 2, 37, 2, 5, 2, 229, 2, 29, 2, 5, 2, 44560482149, 2, 61, 2, 5, 2, 13, 2, 593, 2, 5, 2, 1746860020068409, 2, 11437, 2, 5, 2, 3761, 2, 13, 2, 5, 2, 68480406462161287469, 2, 29, 2, 5, 2

Offset: 2

Author

Sean A. Irvine, Oct 21 2023

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 2..630

Crossrefs

Cf. A246556 (smallest primitive factor), A264137, A280104, A060383, A020639.

Programs

Mathematica

FactorInteger[#][[1, 1]] & /@ LinearRecurrence[{2, 1}, {2, 5}, 57] (* Amiram Eldar, Oct 21 2023 *)

Formula

a(n) = A020639(A000129(n)).