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%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