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A056790 Greatest prime factor of n^n + (n+1)^(n+1). 6
2, 5, 31, 283, 23, 743, 331, 1600069, 410353, 60042893, 8969, 7438489991, 116803, 4879633159, 61215157711, 338142271, 34041259347101651, 45072130459, 6564253087266573169, 22022174223585405703, 121937899012999, 69454092876521107983605569601, 5311242856728321929909 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Note that n^n + (n+1)^(n+1) = A056788(n+1).

Becomes "hard" (unknown) around n ~ 112, cf. link: As of today, even A217435(113) (number of prime factors) is unknown. - M. F. Hasler, Oct 04 2012

As of today, the first unknown term is a(143). - Daniel Suteu, Mar 11 2019

LINKS

Daniel Suteu, Table of n, a(n) for n = 0..142

Walter Nissen, np(n) = n^n + (n+1)^(n+1) -- 2 prominent questions. (Updated Oct 02 2012)

FORMULA

a(n) = A006530(A056788(n+1)). - M. F. Hasler, Oct 04 2012

EXAMPLE

a(4) = 23 because 4^4 + 5^5 = 3381 = 3 * 7^2 * 23.

MATHEMATICA

Join[{2}, FactorInteger[Total[#]][[-1, 1]]&/@Partition[Table[n^n, {n, 30}], 2, 1]] (* Harvey P. Dale, Apr 21 2018 *)

PROG

(PARI) A056790(n)=vecmax(factor((n+1)^(n+1)+n^n)[, 1])  \\ M. F. Hasler, Oct 04 2012

CROSSREFS

Cf. A056187, A192397.

Cf. A217435.

Sequence in context: A032112 A058009 A056187 * A192397 A097396 A056788

Adjacent sequences:  A056787 A056788 A056789 * A056791 A056792 A056793

KEYWORD

nonn,hard

AUTHOR

Walter Nissen, Aug 20 2000

EXTENSIONS

a(0) = 2 added by Arkadiusz Wesolowski, Jun 30 2011

a(21)-a(22) added by Daniel Suteu, Mar 11 2019

STATUS

approved

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Last modified October 17 14:47 EDT 2019. Contains 328114 sequences. (Running on oeis4.)