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 A086075 #10 May 05 2024 19:30:32 %S A086075 0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,0,0, %T A086075 0,0,0,0,1,0,0,0,0,1,0,0,0,0,0,0,0,0,0,1,1,1,0,0,0,0,0,0,0,0,0,1,0,0, %U A086075 1,1,1,0,0,0,0,0,0,0,0,0,1,0,1,1,0,0,1,0,0,1,1,1,1,1,2,1,1,1,1,1,0,0,0,0,1 %N A086075 Number of 4's in decimal expansion of triangular number n(n+1)/2. %H A086075 Paolo Xausa, <a href="/A086075/b086075.txt">Table of n, a(n) for n = 0..10000</a> %t A086075 DigitCount[Accumulate[Range[0, 100]], 10, 4] (* _Paolo Xausa_, May 05 2024 *) %Y A086075 Cf. 0's A086071, 1's A086072, 2's A086073, 3's A086074, 5's A086076, 6's A086077, 7's A086078, 8's A086079, 9's A086080. %K A086075 base,nonn %O A086075 0,95 %A A086075 _Jason Earls_, Jul 08 2003