a(n) = (n + 3)*(n^2 + 6*n + 2)/6.

Terms

a(0) =1a(1) =6a(2) =15a(3) =29a(4) =49a(5) =76a(6) =111a(7) =155a(8) =209a(9) =274a(10) =351a(11) =441a(12) =545a(13) =664a(14) =799a(15) =951a(16) =1121a(17) =1310a(18) =1519a(19) =1749a(20) =2001a(21) =2276a(22) =2575a(23) =2899a(24) =3249a(25) =3626a(26) =4031a(27) =4465a(28) =4929a(29) =5424