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 A209656 #30 Jan 31 2025 17:37:08 %S A209656 1,1,2,4,10,23,63,155,448,1152,3452,9158,28178,76538,240368,665100, %T A209656 2123379,5964156,19301178,54890366,179679030,516360755,1706896545, %U A209656 4949350203,16500278295,48216373545,161946759019,476447428528,1610847688579,4767486352733,16213635060406 %N A209656 Meandric numbers for a river crossing up to 12 parallel roads at n points. %C A209656 Number of ways that a river (or directed line) that starts in the South and flows East can cross up to 12 parallel East-West roads n times. %C A209656 Sequence derived from list of solutions described in A206432. %H A209656 Andrew Howroyd, <a href="/A209656/b209656.txt">Table of n, a(n) for n = 0..40</a> %Y A209656 Column k=12 of A380367. %Y A209656 Cf. A005316 (sequence for one road; extensive references and links). %Y A209656 Cf. A076876 (sequence for two parallel roads). %Y A209656 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 A209656 Cf. A206432 (sequence for unlimited number of parallel roads). %Y A209656 Cf. A076875, A076906, A076907. %K A209656 nonn %O A209656 0,3 %A A209656 _Robert Price_, May 07 2012 %E A209656 a(21) onwards from _Andrew Howroyd_, Jan 31 2025