a(n) = (2*n+1)*(12*n+1).

Terms

a(0) =1a(1) =39a(2) =125a(3) =259a(4) =441a(5) =671a(6) =949a(7) =1275a(8) =1649a(9) =2071a(10) =2541a(11) =3059a(12) =3625a(13) =4239a(14) =4901a(15) =5611a(16) =6369a(17) =7175a(18) =8029a(19) =8931a(20) =9881a(21) =10879a(22) =11925a(23) =13019a(24) =14161a(25) =15351a(26) =16589a(27) =17875a(28) =19209a(29) =20591