A119170 Triangular numbers composed of digits {2,5,9}.

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

Offset: 1

Author

Giovanni Resta, May 10 2006

Keywords

• nonn
• base
• more

Comments

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

Links

• Giovanni Resta, Tridigital Triangular Numbers.

Crossrefs

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

Programs

Mathematica

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

Formula

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

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

Extensions

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