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A237579 Least prime factor of (2n)! - n! + 1 (= A237580(n)). 2
2, 23, 5, 59, 7, 59, 87178286161, 29, 11, 443, 13, 587, 403291461126605629356979201, 3307, 17, 43, 19, 131, 83, 2791, 23, 113, 5502622159812088949850305428800254867109635014075023360001, 659, 761 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

For n=0 the expression equals 1 and has no prime factor at all.

The larger terms, and/or those ending in ...01, correspond to indices (listed in A237443) for which the expression itself is a prime (listed in A118812).

LINKS

Table of n, a(n) for n=1..25.

PROG

(PARI) n -> factor((2*n)!-n!+1)[1, 1]

CROSSREFS

Cf. A237443, A118812.

Sequence in context: A162711 A120713 A167920 * A104644 A158992 A128365

Adjacent sequences:  A237576 A237577 A237578 * A237580 A237581 A237582

KEYWORD

nonn

AUTHOR

M. F. Hasler, Feb 09 2014

STATUS

approved

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Last modified May 25 15:44 EDT 2019. Contains 323572 sequences. (Running on oeis4.)