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 A237580 #18 Sep 08 2022 08:46:06
%S A237580 1,2,23,715,40297,3628681,479000881,87178286161,20922789847681,
%T A237580 6402373705365121,2432902008173011201,1124000727777567763201,
%U A237580 620448401733238960358401,403291461126605629356979201,304888344611713860414325708801,265252859812191058635000805632001
%N A237580 a(n) = (2n)! - n! + 1.
%C A237580 Primes are listed in A118812, the corresponding indices in A237443; the least prime factor of a(n) in A237579.
%H A237580 Vincenzo Librandi, <a href="/A237580/b237580.txt">Table of n, a(n) for n = 0..100</a>
%t A237580 Table[((2 n)! - n! + 1), {n, 0, 30}] (* _Vincenzo Librandi_, Feb 11 2014 *)
%o A237580 (PARI) A237580 = n->(2*n)!-n!+1
%o A237580 (Magma) [Factorial(2*n)-Factorial(n)+1: n in [0..15]]; // _Vincenzo Librandi_, Feb 11 2014
%Y A237580 Cf. A000142 (n!), A010050 ((2n)!)
%K A237580 nonn
%O A237580 0,2
%A A237580 _M. F. Hasler_, Feb 09 2014