Denominator of Sum_{k=0..n} 1/binomial(n,k)^2.

Terms

a(0) =1a(1) =1a(2) =4a(3) =9a(4) =72a(5) =10a(6) =3600a(7) =1575a(8) =2800a(9) =1764a(10) =14112a(11) =13475a(12) =34927200a(13) =2316600a(14) =192192a(15) =4459455a(16) =4994589600a(17) =262061800a(18) =735869534400a(19) =17476901442a(20) =422721728a(21) =353723760a(22) =31127690880a(23) =10150725585