A119039 Triangular numbers composed of digits {0,1,5}.

1, 10, 15, 55, 105, 5050, 5151, 10011, 15051, 105111, 500500, 501501, 505515, 510555, 10015050, 50005000, 50015001, 50055015, 50105055, 51010050, 51111105, 51151555, 110551015, 1051501011, 1505550501, 5000050000, 5000150001, 5000550015, 5001050055, 5010055050

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A058416, A119040. See A119033 for a table of cross-references.

Programs

Magma

[t: n in [1..2*10^7] | Set(Intseq(t)) subset {0,1,5} where t is n*(n+1) div 2]; // Vincenzo Librandi, Dec 18 2015

Mathematica

Rest[Select[FromDigits/@Tuples[{0, 1, 5}, 12], IntegerQ[(Sqrt[8 # + 1] - 1)/2] &]] (* Vincenzo Librandi, Dec 18 2015 *)

Formula

a(n) = A000217(A119040(n)). - Tyler Busby, Mar 31 2023

Extensions

More terms from Vincenzo Librandi, Dec 18 2015