A237579 - OEIS

%I #27 Jun 07 2022 17:17:02

%S 2,23,5,59,7,59,87178286161,29,11,443,13,587,

%T 403291461126605629356979201,3307,17,43,19,131,83,2791,23,113,

%U 5502622159812088949850305428800254867109635014075023360001,659,761,6108689,29,233,31,67,181,25649409970727,1561016461,151,37,223,53,139,41,29209,43,61

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

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

%C 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).

%H Kellen Shenton, <a href="/A237579/b237579.txt">Table of n, a(n) for n = 1..82</a>

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

%Y Cf. A237580, A237443, A118812.

%K nonn

%O 1,1

%A _M. F. Hasler_, Feb 09 2014

%E a(26)-a(42) from _Chai Wah Wu_, Oct 15 2019

%E Typo in a(32) corrected by _Seth A. Troisi_, May 13 2022