A111602 - OEIS

%I #6 Jan 05 2021 22:09:10

%S 1,6,42,300,2475,22050,220500,2381400,28279125,360186750,4970577150,

%T 73045872900,1150472498175,19174541636250,339663308985000,

%U 6333077180430000,124682456989715625,2572020969902133750

%N Third column (m=2) of unsigned triangle A111595.

%F E.g.f.: (1/sqrt(1-x^2))*((x/(1-x))^2)/2!.

%F a(n) = (n!/2!)*Sum_{k=0..floor((n-2)/2)} binomial(2*k, k)*(n-2*k-1)/(4^k), n >= 2.

%K nonn,easy

%O 2,2

%A _Wolfdieter Lang_, Aug 23 2005