A119103 Triangular numbers composed of digits {1,2,6}.

1, 6, 21, 66, 666, 2211, 6216, 212226, 222111, 1222266, 1261666, 16626261, 22121226, 22221111, 121111266, 126222216, 661261161, 2162616261, 2221211226, 2222211111, 21166222626, 66126661611, 166122226621, 216262612611, 222212111226, 222222111111, 22162261612611

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A053883, A119104. See A119033 for a table of cross-references.

Programs

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{1,2,6},n],OddQ[Sqrt[8#+1]]&],{n,12}]] (* Harvey P. Dale, Mar 07 2015 *)

Formula

a(n) = A000217(A119104(n)). - Michel Marcus, Mar 16 2023

Extensions

a(24)-a(27) from Tyler Busby, Mar 14 2023