Four times pentagonal numbers: a(n) = 2*n*(3*n-1).

Terms

a(0) =0a(1) =4a(2) =20a(3) =48a(4) =88a(5) =140a(6) =204a(7) =280a(8) =368a(9) =468a(10) =580a(11) =704a(12) =840a(13) =988a(14) =1148a(15) =1320a(16) =1504a(17) =1700a(18) =1908a(19) =2128a(20) =2360a(21) =2604a(22) =2860a(23) =3128a(24) =3408a(25) =3700a(26) =4004a(27) =4320a(28) =4648a(29) =4988