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A119105 Triangular numbers composed of digits {1,2,7}. 2
1, 21, 171, 1711, 2211, 72771, 121771, 222111, 712221, 22221111, 72222171, 2222211111, 12177127711, 72177771711, 171277217121, 222222111111, 22222221111111, 121727717277211, 2222222211111111, 22117121117271271 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..20.

G. Resta, Tridigital Triangular Numbers

MATHEMATICA

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

CROSSREFS

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

Sequence in context: A241219 A185128 A007261 * A015880 A113163 A090021

Adjacent sequences:  A119102 A119103 A119104 * A119106 A119107 A119108

KEYWORD

nonn,base

AUTHOR

Giovanni Resta, May 10 2006

STATUS

approved

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Last modified July 29 07:00 EDT 2021. Contains 346340 sequences. (Running on oeis4.)