Triangle read by rows: T(n,k) = binomial(4n-k,n-k), 0 <= k <= n.

Terms

a(0) =1a(1) =4a(2) =1a(3) =28a(4) =7a(5) =1a(6) =220a(7) =55a(8) =10a(9) =1a(10) =1820a(11) =455a(12) =91a(13) =13a(14) =1a(15) =15504a(16) =3876a(17) =816a(18) =136a(19) =16a(20) =1a(21) =134596a(22) =33649a(23) =7315a(24) =1330a(25) =190a(26) =19a(27) =1a(28) =1184040a(29) =296010