a(n) = n + 2*binomial(n,2) + 3*binomial(n,3) + 4*binomial(n,4).

Terms

a(0) =0a(1) =1a(2) =4a(3) =12a(4) =32a(5) =75a(6) =156a(7) =294a(8) =512a(9) =837a(10) =1300a(11) =1936a(12) =2784a(13) =3887a(14) =5292a(15) =7050a(16) =9216a(17) =11849a(18) =15012a(19) =18772a(20) =23200a(21) =28371a(22) =34364a(23) =41262a(24) =49152a(25) =58125a(26) =68276a(27) =79704a(28) =92512a(29) =106807