Number triangle T(n,k)=(2n)!/(2k)!.

Terms

a(0) =1a(1) =2a(2) =1a(3) =24a(4) =12a(5) =1a(6) =720a(7) =360a(8) =30a(9) =1a(10) =40320a(11) =20160a(12) =1680a(13) =56a(14) =1a(15) =3628800a(16) =1814400a(17) =151200a(18) =5040a(19) =90a(20) =1a(21) =479001600a(22) =239500800a(23) =19958400a(24) =665280a(25) =11880a(26) =132a(27) =1a(28) =87178291200a(29) =43589145600