A006486 a(n) = largest prime factor of n^n - 1.

3, 13, 17, 71, 43, 4733, 241, 757, 9091, 1806113, 20593, 1803647, 8108731, 39225301, 6700417, 2699538733, 465841, 109912203092239643840221, 222361, 227633407, 285451051007, 1920647391913, 1134793633, 50150933101, 3574533119, 12557612956332313, 1100860153

Offset: 2

Author

Dennis S. Kluk (mathemagician(AT)ameritech.net)

Keywords

• nonn
• hard

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Table of n, a(n) for n = 2..138
• D. S. Kluk and N. J. A. Sloane, Correspondence, 1979.

Crossrefs

Cf. A006530, A007571, A048861, A125135.

Programs

Magma

[Max(PrimeDivisors(n^n-1)):n in [2..28]]; // Marius A. Burtea, Aug 24 2019

Mathematica

Table[Max@Transpose[FactorInteger[n^n - 1]][[1]], {n, 2, 28}] (* Arkadiusz Wesolowski, Aug 06 2012 *)

PARI

for(k=2, 28, my(x=factor(k^k-1), f=x[#x[, 1], 1]); print1(f,", ")) \\ Hugo Pfoertner, Aug 23 2019

Formula

a(n) = A006530(A048861(n)). - Michel Marcus, Aug 24 2019

Extensions

Corrected by T. D. Noe, Nov 14 2006

5 more terms from Arkadiusz Wesolowski, Aug 06 2012

Terms up to a(126) in b-file added by Sean A. Irvine, Apr 25 2017

Terms a(127)-a(138) in b-file added by Max Alekseyev, Aug 26 2021