A086080 - OEIS

A086080

Number of 9's in decimal expansion of triangular number n(n+1)/2.

0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 1, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0

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

OFFSET

0,45

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..65537 [shifted by Georg Fischer, Apr 28 2021]

MATHEMATICA

DigitCount[Accumulate[Range[0, 100]], 10, 9] (* Paolo Xausa, May 05 2024 *)

PROG

(PARI) A086080(n) = length(select(d -> (9==d), digits(binomial(n+1, 2)))); \\ Antti Karttunen, Sep 27 2018; corrected by Georg Fischer Apr 28 2021

CROSSREFS

Cf. A000217.

Cf. 0's A086071, 1's A086072, 2's A086073, 3's A086074, 4's A086075, 5's A086076, 6's A086077, 7's A086078, 8's A086079.