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 A284209 #14 Aug 09 2025 19:40:21 %S A284209 1,7,17,107,341,1799,4161,28123,81925,489335,1131601,7012459,22286421, %T A284209 117469191,273748289,1840690907,5390025989,31943819383,74441889105, %U A284209 461363702635,1465729172821,7728532584199,17872436875329,120787365293531,351860917551109 %N A284209 Decimal representation of generation n in the reversible cellular automaton RCA(3) when started with a single ON cell at generation 0. %H A284209 Robert Price, <a href="/A284209/b284209.txt">Table of n, a(n) for n = 0..999</a> %H A284209 Alan J. Macfarlane, <a href="https://doi.org/10.1088/0305-4470/37/45/006">Linear reversible second-order cellular automata and their first-order matrix equivalents</a>, Journal of Physics A: Mathematical and General 37.45 (2004): 10791. See Fig. 3. %H A284209 Robert Price, <a href="/A284209/a284209.bfile.txt">Diagram of the first 35 generations</a> %H A284209 <a href="/index/Ce#cell">Index entries for sequences related to cellular automata</a> %H A284209 <a href="https://oeis.org/wiki/Index_to_Elementary_Cellular_Automata">Index to Elementary Cellular Automata</a> %e A284209 The second generation (starting at 0) of RCA(3) is x...x where "x" is an ON cell and "." is OFF. Treating this as a binary number yields 10001 which is 17 in decimal notation. Thus a(2) = 17. %Y A284209 Cf. A059319, A284208. %K A284209 nonn %O A284209 0,2 %A A284209 _Robert Price_, Mar 22 2017