A119079 Triangular numbers composed of digits {0,5,6}.

6, 55, 66, 666, 5050, 5565, 6555, 66066, 500500, 600060, 605550, 5656566, 50005000, 60505500, 5000050000, 6050055000, 500000500000, 605000550000, 50000005000000, 60500005500000, 66605656050060, 550006056055665, 555665666566566, 5000000050000000

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers

Crossrefs

Cf. A000217, A058446, A119080. See A119033 for a table of cross-references.

Programs

Mathematica

Rest[Select[FromDigits/@Tuples[{0,5,6},15],IntegerQ[(Sqrt[8#+1]-1)/2]&]] (* Harvey P. Dale, Nov 19 2013 *)

Formula

a(n) = A000217(A119080(n)). - Michel Marcus, Mar 22 2023

Extensions

a(23)-a(24) from Tyler Busby, Mar 22 2023