A372987 - OEIS

%I #9 Jul 13 2024 04:02:41

%S 1,2,6,20,84,360,1848,9360,55440,318240,2106720,13366080,96909120,

%T 668304000,5233092480,38761632000,324451733760,2558267712000,

%U 22711621363200,189311810688000,1771506466329600,15523568476416000,152349556104345600,1397121162877440000

%N a(n) = (2*n)!/(n!*a(n-1)), with a(0)=1.

%F a(n) = Product_{k=0..floor((n-1)/2)} 2*(2*n-4*k-1). - _Andrew Howroyd_, Jul 10 2024

%t a[0] = 1; a[n_] := a[n] = (2n)!/(n!*a[n - 1]);

%t Table[a[n], {n, 0, 30}]

%o (PARI) a(n)=prod(k=0, (n-1)\2, 2*(2*n-4*k-1)) \\ _Andrew Howroyd_, Jul 10 2024

%Y Cf. A372986, A372988.

%K nonn

%O 0,2

%A _Clark Kimberling_, Jul 09 2024