a(n) = Trinomial(2*n+1, 4) = (1/6)*n*(2*n + 1)*(2*n^2 + 9*n + 1), n >= 0.

Terms

a(0) =0a(1) =6a(2) =45a(3) =161a(4) =414a(5) =880a(6) =1651a(7) =2835a(8) =4556a(9) =6954a(10) =10185a(11) =14421a(12) =19850a(13) =26676a(14) =35119a(15) =45415a(16) =57816a(17) =72590a(18) =90021a(19) =110409a(20) =134070a(21) =161336a(22) =192555a(23) =228091a(24) =268324a(25) =313650a(26) =364481a(27) =421245a(28) =484386a(29) =554364