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

Terms

a(0) =0a(1) =3a(2) =18a(3) =45a(4) =84a(5) =135a(6) =198a(7) =273a(8) =360a(9) =459a(10) =570a(11) =693a(12) =828a(13) =975a(14) =1134a(15) =1305a(16) =1488a(17) =1683a(18) =1890a(19) =2109a(20) =2340a(21) =2583a(22) =2838a(23) =3105a(24) =3384a(25) =3675a(26) =3978a(27) =4293a(28) =4620a(29) =4959