A119134 Triangular numbers composed of digits {1,5,7}.

1, 15, 55, 171, 1711, 5151, 11175, 551775, 1777555, 17555775, 51151555, 115117551, 1115171151, 151577151715, 171115717515, 551171777775, 1175175575155, 1577775175717755, 5511171777517575, 7571117555155155, 517577151571517115, 757171775575551115

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A119135. See A119033 for a table of cross-references.

Formula

a(n) = A000217(A119135(n)). - Tyler Busby, Mar 31 2023

Extensions

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