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

1,2

Links

Table of n, a(n) for n=1..21.

Giovanni Resta, Tridigital Triangular Numbers

Formula

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

Mathematica

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

Crossrefs

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

Sequence in context: A019467 A106128 A119186 * A079653 A119063 A119154

Adjacent sequences: A119112 A119113 A119114 * A119116 A119117 A119118

Keyword

nonn,base

Author

Giovanni Resta, May 10 2006

Extensions

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

Status

approved