Triangular numbers (A000217) in A353729.

Terms

a(0) =1a(1) =3a(2) =6a(3) =55a(4) =66a(5) =666a(6) =1128a(7) =1326a(8) =2346a(9) =31626a(10) =133386a(11) =193131a(12) =212226a(13) =236328a(14) =283128a(15) =416328a(16) =881128a(17) =1211346a(18) =1222266a(19) =1466328a(20) =1777555a(21) =2263128a(22) =11293128a(23) =14191128a(24) =16111326a(25) =16316328a(26) =22121226a(27) =22261128a(28) =26263128a(29) =31621128