A119123 Triangular numbers composed of digits {1,4,5}.

1, 15, 45, 55, 5151, 44551, 45451, 1551441, 51141441, 51151555, 114511411, 4141455555, 44144455545, 5541155454555, 54145555454451, 114514415144451, 455441144111551, 1151514555151555, 5144441415145515, 45441555441511411, 444441144541554111, 45545414514441444141

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A053897, A119124. See A119033 for a table of cross-references.

Programs

Mathematica

Select[Flatten[Table[FromDigits/@Tuples[{1,4,5},n],{n,17}]],OddQ[Sqrt[8#+1]]&] (* Harvey P. Dale, Feb 19 2023 *)

Formula

a(n) = A000217(A119124(n)). - Michel Marcus, Mar 23 2023

Extensions

a(21)-a(22) from Tyler Busby, Mar 23 2023