a(n) = 16*n^2 - 4.

Terms

a(0) =12a(1) =60a(2) =140a(3) =252a(4) =396a(5) =572a(6) =780a(7) =1020a(8) =1292a(9) =1596a(10) =1932a(11) =2300a(12) =2700a(13) =3132a(14) =3596a(15) =4092a(16) =4620a(17) =5180a(18) =5772a(19) =6396a(20) =7052a(21) =7740a(22) =8460a(23) =9212a(24) =9996a(25) =10812a(26) =11660a(27) =12540a(28) =13452a(29) =14396