a(n) = n*(5*n+1)/2.

Terms

a(0) =0a(1) =3a(2) =11a(3) =24a(4) =42a(5) =65a(6) =93a(7) =126a(8) =164a(9) =207a(10) =255a(11) =308a(12) =366a(13) =429a(14) =497a(15) =570a(16) =648a(17) =731a(18) =819a(19) =912a(20) =1010a(21) =1113a(22) =1221a(23) =1334a(24) =1452a(25) =1575a(26) =1703a(27) =1836a(28) =1974a(29) =2117