11 times triangular numbers.

Terms

a(0) =0a(1) =11a(2) =33a(3) =66a(4) =110a(5) =165a(6) =231a(7) =308a(8) =396a(9) =495a(10) =605a(11) =726a(12) =858a(13) =1001a(14) =1155a(15) =1320a(16) =1496a(17) =1683a(18) =1881a(19) =2090a(20) =2310a(21) =2541a(22) =2783a(23) =3036a(24) =3300a(25) =3575a(26) =3861a(27) =4158a(28) =4466a(29) =4785