A237580 - 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