a(n) = floor(n^(3/2))*floor(1 + n^(3/2))*floor(2 + n^(3/2))/6.

Terms

a(0) =1a(1) =4a(2) =35a(3) =120a(4) =286a(5) =560a(6) =1140a(7) =2024a(8) =3654a(9) =5456a(10) =8436a(11) =12341a(12) =17296a(13) =24804a(14) =34220a(15) =45760a(16) =59640a(17) =76076a(18) =95284a(19) =121485a(20) =152096a(21) =187460a(22) =227920a(23) =273819a(24) =333375a(25) =392084a(26) =467180a(27) =551300a(28) =644956a(29) =748660