Triangle read by rows: T(n, k) = Sum_{j=0..n} C(j, n-k) * C(j, k) * (-1)^(n - j).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =3a(5) =1a(6) =1a(7) =7a(8) =7a(9) =1a(10) =1a(11) =13a(12) =28a(13) =13a(14) =1a(15) =1a(16) =21a(17) =79a(18) =79a(19) =21a(20) =1a(21) =1a(22) =31a(23) =181a(24) =315a(25) =181a(26) =31a(27) =1a(28) =1a(29) =43