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

1,1

Links

Table of n, a(n) for n=1..17.

Giovanni Resta, Tridigital Triangular Numbers.

Formula

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

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 *)

Crossrefs

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

Sequence in context: A268023 A268016 A077694 * A119236 A126998 A299712

Adjacent sequences: A119213 A119214 A119215 * A119217 A119218 A119219

Keyword

nonn,base

Author

Giovanni Resta, May 10 2006

Extensions

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

Status

approved