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

1,2

Links

Table of n, a(n) for n=1..22.

Giovanni Resta, Tridigital Triangular Numbers

Formula

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

Mathematica

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

Crossrefs

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

Sequence in context: A295980 A029827 A357706 * A293625 A084821 A345654

Adjacent sequences: A119120 A119121 A119122 * A119124 A119125 A119126

Keyword

nonn,base

Author

Giovanni Resta, May 10 2006

Extensions

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

Status

approved