A086080 - OEIS

%I #23 May 05 2024 19:33:11

%S 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,

%T 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,

%U 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

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

%H Antti Karttunen, <a href="/A086080/b086080.txt">Table of n, a(n) for n = 0..65537</a> [shifted by _Georg Fischer_, Apr 28 2021]

%t DigitCount[Accumulate[Range[0, 100]], 10, 9] (* _Paolo Xausa_, May 05 2024 *)

%o (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

%Y Cf. A000217.

%Y 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.

%K base,nonn

%O 0,45

%A _Jason Earls_, Jul 08 2003

%E Zero at the beginning inserted by _Antti Karttunen_, Sep 27 2018

%E Zero at the beginning removed by _Georg Fischer_, Apr 28 2021