a(n) = n*(13*n - 1)/2.

Terms

a(0) =0a(1) =6a(2) =25a(3) =57a(4) =102a(5) =160a(6) =231a(7) =315a(8) =412a(9) =522a(10) =645a(11) =781a(12) =930a(13) =1092a(14) =1267a(15) =1455a(16) =1656a(17) =1870a(18) =2097a(19) =2337a(20) =2590a(21) =2856a(22) =3135a(23) =3427a(24) =3732a(25) =4050a(26) =4381a(27) =4725a(28) =5082a(29) =5452