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
Links
- Giovanni Resta, Tridigital Triangular Numbers.
Programs
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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
Extensions
More terms from Vincenzo Librandi, Dec 18 2015