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 A075273 #28 Mar 09 2025 09:55:10 %S A075273 5,8,37,176,196,1471,6885,5948,60460,280600,199316,2533987,11698223, %T A075273 7080928,107594213,494889092,261542752 %N A075273 Number of reachable arrangements of coins in the game Blet starting with 2n coins. %C A075273 In Blet with 2n coins, we start with 2n coins alternating heads and tails, (HT)^n, in a circle. A move in Blet is either of transitions HTH -> THT or THT -> HTH. This sequence counts the number of arrangements of coins that can be reached by applying these transitions an arbitrary number of times. - _Sean A. Irvine_, Feb 14 2025 %H A075273 Michael S. Branicky, <a href="/A075273/a075273.py.txt">Python program for OEIS A075273</a> %H A075273 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a075/A075273.java">Java program</a> (github) %H A075273 F. Rodriguez Villegas, L. Sadun, and J. F. Voloch, <a href="https://www.jstor.org/stable/3072397">Blet: a mathematical puzzle</a>, Amer. Math. Monthly, 109 No.8 (2002), 729-740. %F A075273 a(n) <= A381814(2*n). - _Pontus von Brömssen_, Mar 08 2025 %e A075273 For 4 coins, starting from HTHT we can reach THTT, HHTH, TTTH, THHH, and no others, hence a(2) = 5. - _Sean A. Irvine_, Feb 14 2025 %o A075273 (Python) # see linked program %Y A075273 Cf. A075274, A381814. %K A075273 nonn,more %O A075273 2,1 %A A075273 _N. J. A. Sloane_, Oct 12 2002 %E A075273 Offset corrected by _Michel Marcus_, Sep 30 2017 %E A075273 a(16)-a(18) from and name clarified by _Sean A. Irvine_, Feb 14 2025