3 times octagonal numbers: a(n) = 3*n*(3*n-2).

Terms

a(0) =0a(1) =3a(2) =24a(3) =63a(4) =120a(5) =195a(6) =288a(7) =399a(8) =528a(9) =675a(10) =840a(11) =1023a(12) =1224a(13) =1443a(14) =1680a(15) =1935a(16) =2208a(17) =2499a(18) =2808a(19) =3135a(20) =3480a(21) =3843a(22) =4224a(23) =4623a(24) =5040a(25) =5475a(26) =5928a(27) =6399a(28) =6888a(29) =7395