A119208 Triangular numbers composed of digits {4,5,9}.

45, 55, 595, 5995, 49455, 55945, 594595, 5559445, 555594445, 9955945495, 55555944445, 95444955595, 5555559444445, 9545454599955, 499594959455595, 549999555454495, 555555594444445, 55555555944444445, 5555555559444444445, 5999995494459499455

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A053955, A119209. See A119033 for a table of cross-references.

Programs

Mathematica

Select[Flatten[Table[FromDigits/@Tuples[{4,5,9},n],{n,17}]],OddQ[ Sqrt[ 8#+1]]&] (* The program will take a long time to run. *) (* Harvey P. Dale, May 23 2021 *)

Formula

a(n) = A000217(A119209(n)). - Tyler Busby, Mar 25 2023

Extensions

a(19)-a(20) from Tyler Busby, Mar 25 2023