Triangular numbers composed of digits {1,7,8}.

Terms

a(0) =1a(1) =78a(2) =171a(3) =1711a(4) =8778a(5) =11781a(6) =887778a(7) =1188111a(8) =18111171a(9) =71778171a(10) =88877778a(11) =811178781a(12) =7781717881a(13) =8888777778a(14) =181877771881a(15) =887788118778a(16) =888887777778