A237579 Least prime factor of (2n)! - n! + 1 (= A237580(n)).

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, 6108689, 29, 233, 31, 67, 181, 25649409970727, 1561016461, 151, 37, 223, 53, 139, 41, 29209, 43, 61

Offset: 1

Author

M. F. Hasler, Feb 09 2014

Keywords

• nonn

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

• Kellen Shenton, Table of n, a(n) for n = 1..82

Crossrefs

Cf. A237580, A237443, A118812.

Programs

PARI

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

Extensions

a(26)-a(42) from Chai Wah Wu, Oct 15 2019

Typo in a(32) corrected by Seth A. Troisi, May 13 2022