a(n) = n*(3*n + 11)/2.

Terms

a(0) =0a(1) =7a(2) =17a(3) =30a(4) =46a(5) =65a(6) =87a(7) =112a(8) =140a(9) =171a(10) =205a(11) =242a(12) =282a(13) =325a(14) =371a(15) =420a(16) =472a(17) =527a(18) =585a(19) =646a(20) =710a(21) =777a(22) =847a(23) =920a(24) =996a(25) =1075a(26) =1157a(27) =1242a(28) =1330a(29) =1421