A119115 Triangular numbers composed of digits {1,3,6}.

1, 3, 6, 36, 66, 136, 666, 13366, 333336, 6631661361, 113113613161, 663363661366, 16116313316131, 633161111666331, 633613661136316, 1331116613613361, 33311633636366361, 663661636336331361, 61163111131316636331, 6313111611636313666666, 1616111661666616161331131

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A053893, A119116. See A119033 for a table of cross-references.

Programs

Mathematica

Table[Select[FromDigits/@Tuples[{1,3,6},n],OddQ[Sqrt[8#+1]]&],{n,18}]//Flatten (* Harvey P. Dale, Sep 18 2017 *)

Formula

a(n) = A000217(A119116(n)). - Michel Marcus, Mar 22 2023

Extensions

a(19)-a(21) from Tyler Busby, Mar 22 2023