Triangular numbers that are repdigits with length > 2 in some base.

Terms

a(0) =15a(1) =21a(2) =91a(3) =171a(4) =666a(5) =703a(6) =820a(7) =1830a(8) =1953a(9) =3003a(10) =3081a(11) =4095a(12) =7140a(13) =7381a(14) =10440a(15) =12720a(16) =14706a(17) =16471a(18) =16653a(19) =18915a(20) =23871a(21) =24976a(22) =30628a(23) =47586a(24) =47895a(25) =48828a(26) =66430a(27) =71631a(28) =79401a(29) =95703