A119121 Triangular numbers composed of digits {1,3,9}.

1, 3, 91, 193131, 9939111, 119993391339919111, 199913191913191191, 399139119131339931, 139191313119199339131, 1313933311991311991139331, 3131199393919119319199931, 31313993393319311993391131311, 1191131333139133131313199933931

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A119122. See A119033 for a table of cross-references.

Formula

a(n) = A000217(A119122(n)).

Extensions

a(13) from Tyler Busby, Mar 28 2023