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 A204352 #23 Jan 31 2025 17:41:27 %S A204352 1,1,2,4,9,21,52,131,345,915,2519,6926,19711,55674,162594,468929, %T A204352 1398129,4100003,12433282,36960316,113678461,341785050,1063890616, %U A204352 3229522688,10156518859,31085477306,98635931623,304048850048,972323924567,3015979607106,9711570455824 %N A204352 Meandric numbers for a river crossing up to 3 parallel roads at n points. %C A204352 Number of ways that a river (or directed line) that starts in the South and flows East can cross 3 parallel East-West roads n times. %C A204352 Sequence derived from list of solutions described in A206432. %H A204352 Andrew Howroyd, <a href="/A204352/b204352.txt">Table of n, a(n) for n = 0..40</a> %Y A204352 Column k=3 of A380367. %Y A204352 Cf. A005316 (sequence for one road; extensive references and links). %Y A204352 Cf. A076876 (sequence for two parallel roads). %Y A204352 Cf. A204352, A208062, A208126, A208452, A208453, A209383, A209621, A209622, A209626, A209656, A209657, A209660, A209707, A210344, A210478, A210567, A210592 (sequences for 3 to 19 parallel roads). %Y A204352 Cf. A206432 (sequence for unlimited number of parallel roads). %Y A204352 Cf. A076875, A076906, A076907. %K A204352 nonn %O A204352 0,3 %A A204352 _Robert Price_, May 07 2012 %E A204352 a(21)-a(40) from _Andrew Howroyd_, Dec 07 2015