Triangular numbers composed of digits {1,5,6}.

Terms

a(0) =1a(1) =6a(2) =15a(3) =55a(4) =66a(5) =561a(6) =666a(7) =5151a(8) =5565a(9) =6555a(10) =55611a(11) =56616a(12) =111156a(13) =511566a(14) =565516a(15) =651511a(16) =1565565a(17) =5556111a(18) =5566116a(19) =5656566a(20) =5666661a(21) =15615666a(22) =16666651a(23) =51151555a(24) =55561611a(25) =61566156a(26) =65111166a(27) =116151661a(28) =555561111a(29) =555661116