3 times 11-gonal (or hendecagonal) numbers: a(n) = 3*n*(9*n-7)/2.

Terms

a(0) =0a(1) =3a(2) =33a(3) =90a(4) =174a(5) =285a(6) =423a(7) =588a(8) =780a(9) =999a(10) =1245a(11) =1518a(12) =1818a(13) =2145a(14) =2499a(15) =2880a(16) =3288a(17) =3723a(18) =4185a(19) =4674a(20) =5190a(21) =5733a(22) =6303a(23) =6900a(24) =7524a(25) =8175a(26) =8853a(27) =9558a(28) =10290a(29) =11049