Triangular numbers composed of digits {1,2,7}.

Terms

a(0) =1a(1) =21a(2) =171a(3) =1711a(4) =2211a(5) =72771a(6) =121771a(7) =222111a(8) =712221a(9) =22221111a(10) =72222171a(11) =2222211111a(12) =12177127711a(13) =72177771711a(14) =171277217121a(15) =222222111111