Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #18 Sep 08 2022 08:46:06
%S 1,2,23,715,40297,3628681,479000881,87178286161,20922789847681,
%T 6402373705365121,2432902008173011201,1124000727777567763201,
%U 620448401733238960358401,403291461126605629356979201,304888344611713860414325708801,265252859812191058635000805632001
%N a(n) = (2n)! - n! + 1.
%C Primes are listed in A118812, the corresponding indices in A237443; the least prime factor of a(n) in A237579.
%H Vincenzo Librandi, <a href="/A237580/b237580.txt">Table of n, a(n) for n = 0..100</a>
%t Table[((2 n)! - n! + 1), {n, 0, 30}] (* _Vincenzo Librandi_, Feb 11 2014 *)
%o (PARI) A237580 = n->(2*n)!-n!+1
%o (Magma) [Factorial(2*n)-Factorial(n)+1: n in [0..15]]; // _Vincenzo Librandi_, Feb 11 2014
%Y Cf. A000142 (n!), A010050 ((2n)!)
%K nonn
%O 0,2
%A _M. F. Hasler_, Feb 09 2014