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

Terms

a(0) =-1a(1) =-1a(2) =11a(3) =35a(4) =71a(5) =119a(6) =179a(7) =251a(8) =335a(9) =431a(10) =539a(11) =659a(12) =791a(13) =935a(14) =1091a(15) =1259a(16) =1439a(17) =1631a(18) =1835a(19) =2051a(20) =2279a(21) =2519a(22) =2771a(23) =3035a(24) =3311a(25) =3599a(26) =3899a(27) =4211a(28) =4535a(29) =4871