A274907 Largest prime factor of 6^n - 1.

5, 7, 43, 37, 311, 43, 55987, 1297, 2467, 311, 3154757, 97, 760891, 55987, 1201, 98801, 30839, 46441, 638073026189, 6781, 1822428931, 51828151, 7505944891, 1678321, 40185601, 760891, 623067280651, 5030761, 7369130657357778596659, 1950271, 49744740983476472807

Offset

1,1

Links

Amiram Eldar, Table of n, a(n) for n = 1..420 (terms 1..100 from Vincenzo Librandi)

J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.

Formula

a(n) = A006530(A024062(n)). - Michel Marcus, Jul 11 2016

Example

6^5 - 1 = 7775 = 5*5*311, so a(5) = 311.

Mathematica

Table[FactorInteger[6^n - 1][[-1, 1]], {n, 40}]

Prog

(Magma) [Maximum(PrimeDivisors(6^n-1)): n in [1..40]];
(PARI) a(n) = vecmax(factor(6^n-1)[, 1]); \\ Michel Marcus, Jul 13 2016

Crossrefs

Cf. A006530, A024062.

Cf. similar sequences listed in A274906.

Sequence in context: A234040 A292010 A064082 * A213175 A265786 A090520

Adjacent sequences: A274904 A274905 A274906 * A274908 A274909 A274910

Keyword

nonn

Author

Vincenzo Librandi, Jul 11 2016

Status

approved