Hexagonal numbers: a(n) = n*(2*n-1).

Terms

a(0) =0a(1) =1a(2) =6a(3) =15a(4) =28a(5) =45a(6) =66a(7) =91a(8) =120a(9) =153a(10) =190a(11) =231a(12) =276a(13) =325a(14) =378a(15) =435a(16) =496a(17) =561a(18) =630a(19) =703a(20) =780a(21) =861a(22) =946a(23) =1035a(24) =1128a(25) =1225a(26) =1326a(27) =1431a(28) =1540a(29) =1653