A094474 a(n) is the largest prime factor of 2^n + 3^n.

5, 13, 7, 97, 11, 61, 463, 401, 577, 4621, 35839, 5521, 4057, 369181, 241, 14177, 7039, 181, 555029, 3121, 92233, 2414250301, 13249, 41432641, 513101, 13761229, 377604937, 3001769, 148466603, 24001, 22674269, 1607133116929, 22270249, 1282861452271981, 392943879511

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..546 (terms 1..120 from Vincenzo Librandi)

Formula

a(n) = A006530(A007689(n)). - Amiram Eldar, Dec 27 2019

Example

n = 100, 2^100 + 3^100 = 41 * 97 * 281 * 3121 * 742801 * 20017001 * 9937984196743741414107401 so a(100) = 9937984196743741414107401.

Mathematica

Table[Part[Reverse[Flatten[FactorInteger[2^w + 3^w]]], 2], {w, 1, 100}]

Prog

(Magma) [Max(PrimeFactors(2^n + 3^n)):n in[1..68]]; // Vincenzo Librandi, Dec 25 2019

Crossrefs

Cf. A006530, A007689.

Sequence in context: A340802 A088315 A138296 * A064109 A175484 A210694

Adjacent sequences: A094471 A094472 A094473 * A094475 A094476 A094477

Keyword

nonn

Author

Labos Elemer, Jun 01 2004

Extensions

a(34)-a(35) from Vincenzo Librandi, Dec 25 2019

Status

approved