a(n) = ( 2*n*(2*n^2 + 9*n + 14) + (-1)^n - 1 )/16.

Terms

a(0) =0a(1) =3a(2) =10a(3) =22a(4) =41a(5) =68a(6) =105a(7) =153a(8) =214a(9) =289a(10) =380a(11) =488a(12) =615a(13) =762a(14) =931a(15) =1123a(16) =1340a(17) =1583a(18) =1854a(19) =2154a(20) =2485a(21) =2848a(22) =3245a(23) =3677a(24) =4146a(25) =4653a(26) =5200a(27) =5788a(28) =6419a(29) =7094