a(n) = n*(2*n-3).

Terms

a(0) =0a(1) =-1a(2) =2a(3) =9a(4) =20a(5) =35a(6) =54a(7) =77a(8) =104a(9) =135a(10) =170a(11) =209a(12) =252a(13) =299a(14) =350a(15) =405a(16) =464a(17) =527a(18) =594a(19) =665a(20) =740a(21) =819a(22) =902a(23) =989a(24) =1080a(25) =1175a(26) =1274a(27) =1377a(28) =1484a(29) =1595