Twice nonagonal numbers (or twice 9-gonal numbers): a(n) = n*(7*n-5).

Terms

a(0) =0a(1) =2a(2) =18a(3) =48a(4) =92a(5) =150a(6) =222a(7) =308a(8) =408a(9) =522a(10) =650a(11) =792a(12) =948a(13) =1118a(14) =1302a(15) =1500a(16) =1712a(17) =1938a(18) =2178a(19) =2432a(20) =2700a(21) =2982a(22) =3278a(23) =3588a(24) =3912a(25) =4250a(26) =4602a(27) =4968a(28) =5348a(29) =5742