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 A031232 #6 Apr 26 2019 09:47:42 %S A031232 1,0,0,0,1,1,2,3,4,3,4,4,5,5,4,4,3,4,3,2,1,1,0,0,0,0,0,1,1,0,0,0,0,0, %T A031232 0,0,0,1,1,0,0,0,0,0,1,1,1,2,2,3,4,4,3,4,4,4,5,5,5,6,7,7,8,9,10,11,12, %U A031232 11,12,13,13,14,15,15,16,15,15,16,15,16,17,16 %N A031232 a(n)=(# 1's)-(# 2's) in first n terms of A031219. %t A031232 Accumulate[Which[#==1,1,#==2,-1,True,0]&/@Flatten@IntegerDigits[ Range@ 40,5]] (* _Harvey P. Dale_, Apr 26 2019 *) %K A031232 nonn %O A031232 1,7 %A A031232 _Clark Kimberling_