A119043 Triangular numbers composed of digits {0,1,7}.

1, 10, 171, 1711, 1770, 10011, 111117701071, 17170010070077710, 101711101707777771, 701000700077010700, 1701111717707771071, 10010107100007777700, 101770070070071771070, 170107111111710707070, 1177170070777107111711, 70071707101001717077017171

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

Cf. A000217, A058420, A119044. See A119033 for a table of cross-references.

Programs

Mathematica

Select[FromDigits/@Tuples[{0,1,7},12],OddQ[Sqrt[8#+1]]&] (* The program generates the first 8 terms of the sequence. *) (* Harvey P. Dale, Sep 06 2022 *)

Formula

a(n) = A000217(A119044(n)). - Tyler Busby, Mar 31 2023

Extensions

a(15)-a(16) from Tyler Busby, Mar 22 2023