a(n) = n*(25*n + 1)/2.

Terms

a(0) =0a(1) =13a(2) =51a(3) =114a(4) =202a(5) =315a(6) =453a(7) =616a(8) =804a(9) =1017a(10) =1255a(11) =1518a(12) =1806a(13) =2119a(14) =2457a(15) =2820a(16) =3208a(17) =3621a(18) =4059a(19) =4522a(20) =5010a(21) =5523a(22) =6061a(23) =6624a(24) =7212a(25) =7825a(26) =8463a(27) =9126a(28) =9814a(29) =10527