A119109 Triangular numbers composed of digits {1,2,9}.

1, 21, 91, 2211, 222111, 22221111, 229119121, 291212911, 2222211111, 222222111111, 299992122991, 1122921211191, 22222221111111, 2222222211111111, 21212929921912191, 222222222111111111, 22222222221111111111, 2222222222211111111111, 191929912211129991991191

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A053889, A119110. See A119033 for a table of cross-references.

Formula

a(n) = A000217(A119110(n)). - Tyler Busby, Mar 31 2023

Extensions

a(17)-a(19) from Tyler Busby, Mar 22 2023