a(n) = n*(67*n - 89)/2.

Terms

a(0) =0a(1) =-11a(2) =45a(3) =168a(4) =358a(5) =615a(6) =939a(7) =1330a(8) =1788a(9) =2313a(10) =2905a(11) =3564a(12) =4290a(13) =5083a(14) =5943a(15) =6870a(16) =7864a(17) =8925a(18) =10053a(19) =11248a(20) =12510a(21) =13839a(22) =15235a(23) =16698a(24) =18228a(25) =19825a(26) =21489a(27) =23220a(28) =25018a(29) =26883