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 A339449 #11 Dec 21 2020 07:41:21 %S A339449 0,4,386,398,2919434,2919644,2919648 %N A339449 Numbers k such that there are equal numbers of 0's and 2's and equal numbers of 1's and 3's among the first k digits of the quaternary representation of Pi. %C A339449 The terms can also be interpreted as numbers k such that a walk on the square lattice governed by the quaternary digits of Pi is at the origin after k steps, where digit 0 corresponds to a step to the right, 1 to up, 2 to left, and 3 to down. %C A339449 There are no more terms below 2*10^9. %C A339449 There are two variations of this sequence, according to the directions each digit corresponds to. In A339450, 0=right, 1=left, 2=up, 3=down. For the case 0=right, 1=up, 2=down, 3=left, the only terms below 2*10^9 are 0, 2, 4, 8. %e A339449 4 is a term because the first four quaternary digits of Pi are 3, 0, 2, 1, one of each digit. %e A339449 386 is a term because among the first 386 digits there are 99 0's and 99 2's, and 94 1's and 94 3's. %Y A339449 Cf. A004603, A039624, A339450. %K A339449 nonn,base,more %O A339449 1,2 %A A339449 _Pontus von Brömssen_, Dec 05 2020