A337429 a(n) is the largest prime factor of 2^n + 5^n.

2, 7, 29, 19, 641, 41, 541, 1597, 22993, 397, 5521, 303293, 380881, 25117, 210466621, 508771, 1573071713, 108991369171, 1343341, 2724783836059, 39558401, 2525293, 4807441, 215038823, 1173553, 61001, 16463734208221, 3813697527769, 58116853330557841, 327866809, 99901

Offset

0,1

Links

Amiram Eldar, Table of n, a(n) for n = 0..387 (terms 0..200 from Hugo Pfoertner)

Formula

a(n) = A006530(A074600(n)).

Mathematica

a[n_] := FactorInteger[2^n + 5^n][[-1, 1]]; Array[a, 31, 0] (* Amiram Eldar, Mar 30 2023 *)

Prog

(PARI) for(n=0, 30, my(p=2^n+5^n); print1(vecmax(factor(p)[, 1]), ", "))

Crossrefs

Cf. A006530, A074600, A094474, A094475, A122118.

Sequence in context: A191478 A321181 A122118 * A059803 A076043 A180448

Adjacent sequences: A337426 A337427 A337428 * A337430 A337431 A337432

Keyword

nonn

Author

Hugo Pfoertner, Sep 23 2020

Status

approved