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 A209657 #20 Jan 31 2025 17:36:58 %S A209657 1,1,2,4,10,23,63,155,448,1152,3452,9158,28178,76539,240369,665127, %T A209657 2123408,5964627,19301713,54897139,179687084,516448412,1707004865, %U A209657 4950415081,16501638058,48228801029,161963084065,476588705579,1611037922998,4769064680579,16215807145689 %N A209657 Meandric numbers for a river crossing up to 13 parallel roads at n points. %C A209657 Number of ways that a river (or directed line) that starts in the South and flows East can cross up to 13 parallel East-West roads n times. %C A209657 Sequence derived from list of solutions described in A206432. %H A209657 Andrew Howroyd, <a href="/A209657/b209657.txt">Table of n, a(n) for n = 0..40</a> %Y A209657 Column k=13 of A380367. %Y A209657 Cf. A005316 (sequence for one road; extensive references and links). %Y A209657 Cf. A076876 (sequence for two parallel roads). %Y A209657 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 A209657 Cf. A206432 (sequence for unlimited number of parallel roads). %Y A209657 Cf. A076875, A076906, A076907. %K A209657 nonn %O A209657 0,3 %A A209657 _Robert Price_, May 07 2012 %E A209657 a(21) onwards from _Andrew Howroyd_, Jan 31 2025