a(n) = (2*n^3 + 5*n^2 - 3*n)/2.

Terms

a(0) =2a(1) =15a(2) =45a(3) =98a(4) =180a(5) =297a(6) =455a(7) =660a(8) =918a(9) =1235a(10) =1617a(11) =2070a(12) =2600a(13) =3213a(14) =3915a(15) =4712a(16) =5610a(17) =6615a(18) =7733a(19) =8970a(20) =10332a(21) =11825a(22) =13455a(23) =15228a(24) =17150a(25) =19227a(26) =21465a(27) =23870a(28) =26448a(29) =29205