G.f.: Sum_{n>=0} (n+1)*(n+2)/2 * (x + x^n)^n.

Terms

a(0) =1a(1) =6a(2) =6a(3) =22a(4) =21a(5) =51a(6) =28a(7) =126a(8) =45a(9) =170a(10) =156a(11) =246a(12) =91a(13) =627a(14) =120a(15) =496a(16) =588a(17) =876a(18) =190a(19) =1626a(20) =231a(21) =1776a(22) =1536a(23) =1392a(24) =325a(25) =4977a(26) =798a(27) =2086a(28) =3405a(29) =5025