A053885 -id:A053885 - cp's OEIS frontend

A119105 Triangular numbers composed of digits {1,2,7}.

1, 21, 171, 1711, 2211, 72771, 121771, 222111, 712221, 22221111, 72222171, 2222211111, 12177127711, 72177771711, 171277217121, 222222111111, 22222221111111, 121727717277211, 2222222211111111, 22117121117271271, 222222222111111111, 12172172111271712221

Offset: 1

Giovanni Resta, May 10 2006

Giovanni Resta, Tridigital Triangular Numbers.

Cf. A000217, A053885, A119106. See A119033 for a table of cross-references.

Flatten[Table[Select[FromDigits/@Tuples[{1,2,7},n],OddQ[Sqrt[8#+1]]&],{n,17}]] (* Harvey P. Dale, Sep 02 2015 *)

a(n) = A000217(A119106(n)). - Tyler Busby, Mar 31 2023

a(21)-a(22) from Tyler Busby, Mar 23 2023

A053884 Numbers k such that k^2 contains only digits {1,2,7}.

Original entry on oeis.org

1, 11, 1489, 4596489, 4144600242739, 130834904430015239

Offset: 1

Patrick De Geest, Mar 15 2000

P. De Geest, Squares containing at most three distinct digits, Index entries for related sequences
Hisanori Mishima, Sporadic tridigital solutions

Cf. A053885.

One more term from Jon E. Schoenfield, Sep 03 2006

One more term from Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 23 2007

cp's OEIS Frontend

A119105 Triangular numbers composed of digits {1,2,7}.

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