dot product (n,n-1,...2,1).(3,4,...,n,1,2).

Terms

a(0) =13a(1) =28a(2) =50a(3) =80a(4) =119a(5) =168a(6) =228a(7) =300a(8) =385a(9) =484a(10) =598a(11) =728a(12) =875a(13) =1040a(14) =1224a(15) =1428a(16) =1653a(17) =1900a(18) =2170a(19) =2464a(20) =2783a(21) =3128a(22) =3500a(23) =3900a(24) =4329a(25) =4788a(26) =5278a(27) =5800a(28) =6355a(29) =6944