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

Offset: 0

Author

Jason Earls, Jul 08 2003

Keywords

• base
• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 0..65537 [shifted 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.

Programs

Mathematica

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

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

Extensions

Zero at the beginning inserted by Antti Karttunen, Sep 27 2018

Zero at the beginning removed by Georg Fischer, Apr 28 2021