This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A086080 #23 May 05 2024 19:33:11 %S A086080 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 A086080 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 A086080 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 A086080 Number of 9's in decimal expansion of triangular number n(n+1)/2. %H A086080 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 A086080 DigitCount[Accumulate[Range[0, 100]], 10, 9] (* _Paolo Xausa_, May 05 2024 *) %o A086080 (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 A086080 Cf. A000217. %Y A086080 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 A086080 base,nonn %O A086080 0,45 %A A086080 _Jason Earls_, Jul 08 2003 %E A086080 Zero at the beginning inserted by _Antti Karttunen_, Sep 27 2018 %E A086080 Zero at the beginning removed by _Georg Fischer_, Apr 28 2021