3 times heptagonal numbers: a(n) = 3*n*(5*n-3)/2.

Terms

a(0) =0a(1) =3a(2) =21a(3) =54a(4) =102a(5) =165a(6) =243a(7) =336a(8) =444a(9) =567a(10) =705a(11) =858a(12) =1026a(13) =1209a(14) =1407a(15) =1620a(16) =1848a(17) =2091a(18) =2349a(19) =2622a(20) =2910a(21) =3213a(22) =3531a(23) =3864a(24) =4212a(25) =4575a(26) =4953a(27) =5346a(28) =5754a(29) =6177