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A094474 a(n) is the largest prime factor of 2^n + 3^n. 6
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 (list; graph; refs; listen; history; text; internal format)
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: A068530 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

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Last modified August 13 22:57 EDT 2020. Contains 336473 sequences. (Running on oeis4.)