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a(n) = (3*n+1)!.
2

%I #10 Jun 23 2020 06:16:13

%S 1,24,5040,3628800,6227020800,20922789888000,121645100408832000,

%T 1124000727777607680000,15511210043330985984000000,

%U 304888344611713860501504000000,8222838654177922817725562880000000

%N a(n) = (3*n+1)!.

%F Sum_{n>=0} 1/a(n) = A143820. - _Amiram Eldar_, Jun 23 2020

%p seq( (3*n+1)!,n=0..13);

%t Table[(3*n+1)!, {n, 0, 10}] (* _Amiram Eldar_, Jun 23 2020 *)

%Y Cf. A000142, A143820.

%K nonn

%O 0,2

%A _Jorge Coveiro_, Dec 26 2004

%E Offset 0 and a(0) added by _Amiram Eldar_, Jun 23 2020