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 A308638 #12 Jun 18 2019 11:58:09 %S A308638 0,0,0,1,0,1,0,1,1,0,0,1,2,3,1,1,1,1,3,0,1,2,3,1,4,2,1,3,2,4,1,1,2,2, %T A308638 2,3,3,4,2,3,3,2,4,4,0,1,3,2,1,3,4,5,3,6,5,3,2,6,0,3,6,4,0,3,5,5,5,4, %U A308638 3,6,3,3,7,3,2,3,3,2,2,1,3,5,6,4,2,4,5 %N A308638 a(n) is the number of k > 0 such that n-1-2*k > 0 and the points (n-1-2*k, a(n-1-2*k)), (n-1-k, a(n-1-k)) and (n-1, a(n-1)) are aligned. %C A308638 Is this sequence bounded? %C A308638 Are there infinitely many null values? %H A308638 Rémy Sigrist, <a href="/A308638/b308638.txt">Table of n, a(n) for n = 1..10000</a> %H A308638 Rémy Sigrist, <a href="/A308638/a308638.png">Scatterplot of the first 25000000 terms</a> %H A308638 Rémy Sigrist, <a href="/A308638/a308638.txt">C program for A308638</a> %e A308638 The first terms, alongside the values of k such that (n-1-2*k, a(n-1-2*k)), (n-1-k, a(n-1-k)) and (n-1, a(n-1)), are: %e A308638 n a(n) k's %e A308638 -- ---- ----- %e A308638 1 0 none %e A308638 2 0 none %e A308638 3 0 none %e A308638 4 1 1 %e A308638 5 0 none %e A308638 6 1 2 %e A308638 7 0 none %e A308638 8 1 2 %e A308638 9 1 2 %e A308638 10 0 none %e A308638 11 0 none %e A308638 12 1 4 %e A308638 13 2 3,4 %e A308638 14 3 1,4,5 %o A308638 (C) See Links section. %Y A308638 See A308639 for a similar sequence. %K A308638 nonn,look %O A308638 1,13 %A A308638 _Rémy Sigrist_, Jun 13 2019