a(n) = (2*n+1)*(6*n-1).

Terms

a(0) =-1a(1) =15a(2) =55a(3) =119a(4) =207a(5) =319a(6) =455a(7) =615a(8) =799a(9) =1007a(10) =1239a(11) =1495a(12) =1775a(13) =2079a(14) =2407a(15) =2759a(16) =3135a(17) =3535a(18) =3959a(19) =4407a(20) =4879a(21) =5375a(22) =5895a(23) =6439a(24) =7007a(25) =7599a(26) =8215a(27) =8855a(28) =9519a(29) =10207