A053929 -id:A053929

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A119170

Triangular numbers composed of digits {2,5,9}.

+10
2

55, 595, 5995, 255255, 292995, 299925, 25952229225, 99292929555225, 55955525255559595, 555959229929999252295, 925952955522559552259925, 5299552922255552929595999295, 5995959559225555222929295255522595295, 9925559955529295222599225259529552225

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

COMMENTS

a(15) > 10^40. - Tyler Busby, Mar 24 2023

LINKS

Table of n, a(n) for n=1..14.

Giovanni Resta, Tridigital Triangular Numbers.

FORMULA

a(n) = A000217(A119171(n)).

a(n) == 5 (mod 10) for all n. - Chai Wah Wu, Nov 30 2018

MATHEMATICA

Flatten[Table[Select[FromDigits /@ Tuples[{2, 5, 9}, n], IntegerQ[(Sqrt[8 # + 1] - 1)/2] &], {n, 11}]] (* Amiram Eldar, Nov 30 2018 *)

CROSSREFS

Cf. A000217, A053929, A119171. See A119033 for a table of cross-references.

KEYWORD

nonn,base,more

AUTHOR

Giovanni Resta, May 10 2006

EXTENSIONS

a(13)-a(14) from Tyler Busby, Mar 24 2023

STATUS

approved

A053928

Numbers k such that k^2 contains only digits {2,5,9}.

+10
1

3, 5, 15, 23, 77, 173, 235, 315, 1515, 2435, 7227, 23515, 54335, 97773, 243515, 2435077, 3090673, 72497765, 74533585, 9639636523, 979793819766485, 77170285247817565, 9794365502654705173, 1598601020441309256565, 30484348812550551609088485, 76975943837016723668817565

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..26.

P. De Geest, Squares containing at most three distinct digits, Index entries for related sequences

Author?, Source, (txt)

H. Mishima, Sporadic tridigital solutions

CROSSREFS

Cf. A053929.

KEYWORD

nonn,base