Triangle, read by rows, where T(n,k) = C( n*(n+1)/2 + n-k + 2, n-k), for n>=k>=0.

Terms

a(0) =1a(1) =4a(2) =1a(3) =21a(4) =6a(5) =1a(6) =165a(7) =45a(8) =9a(9) =1a(10) =1820a(11) =455a(12) =91a(13) =13a(14) =1a(15) =26334a(16) =5985a(17) =1140a(18) =171a(19) =18a(20) =1a(21) =475020a(22) =98280a(23) =17550a(24) =2600a(25) =300a(26) =24a(27) =1a(28) =10295472a(29) =1947792