a(n) = 7*n^2/2 + 3*n/2 + 1.

Terms

a(0) =1a(1) =6a(2) =18a(3) =37a(4) =63a(5) =96a(6) =136a(7) =183a(8) =237a(9) =298a(10) =366a(11) =441a(12) =523a(13) =612a(14) =708a(15) =811a(16) =921a(17) =1038a(18) =1162a(19) =1293a(20) =1431a(21) =1576a(22) =1728a(23) =1887a(24) =2053a(25) =2226a(26) =2406a(27) =2593a(28) =2787a(29) =2988