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 A086074 #7 Dec 15 2017 17:36:32 %S A086074 0,0,1,0,0,0,0,0,1,0,0,0,0,0,0,0,1,1,0,0,0,1,1,0,1,1,1,1,0,1,0,0,0,0, %T A086074 0,1,0,1,0,0,0,0,1,0,0,1,0,0,0,0,0,1,1,1,0,0,0,1,0,0,1,0,1,0,0,0,0,0, %U A086074 1,0,0,0,0,0,0,0,0,2,1,1,1,2,2,1,1,1,1,1,1,0,0,0,0,1,0,0,0,1,0,0,0,0,1,1,0 %N A086074 Number of 3's in decimal expansion of triangular number n(n+1)/2. %t A086074 DigitCount[#,10,3]&/@Accumulate[Range[0,110]] (* _Harvey P. Dale_, Aug 01 2017 *) %Y A086074 Cf. 0's A086071, 1's A086072, 2's A086073, 4's A086075, 5's A086076, 6's A086077, 7's A086078, 8's A086079, 9's A086080. %K A086074 base,nonn %O A086074 0,78 %A A086074 _Jason Earls_, Jul 08 2003