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

0,45

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.

Sequence in context: A071164 A027345 A328959 * A369054 A281477 A070139

Adjacent sequences: A086077 A086078 A086079 * A086081 A086082 A086083

Keyword

base,nonn

Author

Jason Earls, Jul 08 2003

Extensions

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

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

Status

approved