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 A350784 #41 Jan 06 2025 22:29:39 %S A350784 1,2,2,12,8,44,192,2688,1344,6896,24228,316848,812624,9158880, %T A350784 75652512,1813091520,725236608,3568226496,11152502816,137997707616, %U A350784 309878131724 %N A350784 Number of Gray code sequences of length 2*n where numbers are between 0 and 2*n-1. %C A350784 The sequences are given with the first term as zero. %H A350784 Thomas König, <a href="/A350784/a350784_1.f90.txt">Fortran program for calculating the sequence</a> %H A350784 Wikipedia, <a href="https://en.wikipedia.org/wiki/Gray_code">Gray code</a> %H A350784 Wikipedia, <a href="https://en.wikipedia.org/wiki/Hamming_distance">Hamming distance</a> %F A350784 a(2^m) = A003042(m+1). %F A350784 a(n) = 2 * A236602(n) for n >= 2. - _Alois P. Heinz_, Feb 01 2022 %e A350784 The following Gray codes of length 10 contain only the numbers between 0 and 9: %e A350784 0, 2, 3, 7, 6, 4, 5, 1, 9, 8; %e A350784 0, 2, 6, 4, 5, 7, 3, 1, 9, 8; %e A350784 0, 4, 5, 7, 6, 2, 3, 1, 9, 8; %e A350784 0, 4, 6, 2, 3, 7, 5, 1, 9, 8; %e A350784 0, 8, 9, 1, 3, 2, 6, 7, 5, 4; %e A350784 0, 8, 9, 1, 3, 7, 5, 4, 6, 2; %e A350784 0, 8, 9, 1, 5, 4, 6, 7, 3, 2; %e A350784 0, 8, 9, 1, 5, 7, 3, 2, 6, 4. %e A350784 Therefore a(5) = 8. %o A350784 (Fortran) ! See König link. %Y A350784 Cf. A003042 (a subsequence), A003188, A236602, A290772. %K A350784 nonn,hard,more %O A350784 1,2 %A A350784 _Thomas König_, Jan 16 2022 %E A350784 a(17)-a(18) (via A236602) from _Alois P. Heinz_, Feb 01 2022 %E A350784 a(19)-a(20) from _Martin Ehrenstein_, Feb 16 2022 %E A350784 a(21) from _Martin Ehrenstein_, Feb 21 2022