A119216 Triangular numbers composed of digits {4,7,8}.

78, 8778, 448878, 887778, 7478778, 88877778, 8888777778, 44847878778, 747488474778, 888887777778, 88888877777778, 8888888777777778, 888888887777777778, 7778777484477877878, 88888888877777777778, 7444484774887874784778, 8888888888777777777778

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A053963, A119217. See A119033 for a table of cross-references.

Programs

Mathematica

Table[Select[FromDigits/@Tuples[{4,7,8},n],OddQ[Sqrt[8#+1]]&],{n,20}]//Flatten (* The program will take a long time to run. *) (* Harvey P. Dale, Oct 15 2017 *)

Formula

a(n) = A000217(A119217(n)). - Tyler Busby, Mar 26 2023

Extensions

a(16)-a(17) from Tyler Busby, Mar 26 2023