This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A237579 #27 Jun 07 2022 17:17:02 %S A237579 2,23,5,59,7,59,87178286161,29,11,443,13,587, %T A237579 403291461126605629356979201,3307,17,43,19,131,83,2791,23,113, %U A237579 5502622159812088949850305428800254867109635014075023360001,659,761,6108689,29,233,31,67,181,25649409970727,1561016461,151,37,223,53,139,41,29209,43,61 %N A237579 Least prime factor of (2n)! - n! + 1 (= A237580(n)). %C A237579 For n=0 the expression equals 1 and has no prime factor at all. %C A237579 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 A237579 Kellen Shenton, <a href="/A237579/b237579.txt">Table of n, a(n) for n = 1..82</a> %o A237579 (PARI) n -> factor((2*n)!-n!+1)[1,1] %Y A237579 Cf. A237580, A237443, A118812. %K A237579 nonn %O A237579 1,1 %A A237579 _M. F. Hasler_, Feb 09 2014 %E A237579 a(26)-a(42) from _Chai Wah Wu_, Oct 15 2019 %E A237579 Typo in a(32) corrected by _Seth A. Troisi_, May 13 2022