A119132 Triangular numbers composed of digits {1,5,6}.

1, 6, 15, 55, 66, 561, 666, 5151, 5565, 6555, 55611, 56616, 111156, 511566, 565516, 651511, 1565565, 5556111, 5566116, 5656566, 5666661, 15615666, 16666651, 51151555, 55561611, 61566156, 65111166, 116151661, 555561111, 555661116, 556561566, 556661661

Offset

1,2

Links

Table of n, a(n) for n=1..32.

Giovanni Resta, Tridigital Triangular Numbers.

Formula

a(n) = A000217(A119133(n)). - Tyler Busby, Mar 31 2023

Mathematica

Select[FromDigits/@Flatten[Table[Tuples[{1, 5, 6}, n], {n, 9}], 1], OddQ[ Sqrt[ 8#+1]]&] (* Harvey P. Dale, Jul 25 2015 *)

Crossrefs

Cf. A000217, A053903, A119133. See A119033 for a table of cross-references.

Sequence in context: A244024 A122365 A262912 * A073065 A190801 A093042

Adjacent sequences: A119129 A119130 A119131 * A119133 A119134 A119135

Keyword

nonn,base

Author

Giovanni Resta, May 10 2006

Extensions

a(31)-a(32) from Tyler Busby, Mar 23 2023

Status

approved