a(n) = (4*n^3 + 12*n^2 - 4*n + 3)/3.

Terms

a(0) =1a(1) =5a(2) =25a(3) =69a(4) =145a(5) =261a(6) =425a(7) =645a(8) =929a(9) =1285a(10) =1721a(11) =2245a(12) =2865a(13) =3589a(14) =4425a(15) =5381a(16) =6465a(17) =7685a(18) =9049a(19) =10565a(20) =12241a(21) =14085a(22) =16105a(23) =18309a(24) =20705a(25) =23301a(26) =26105a(27) =29125a(28) =32369a(29) =35845