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%I #20 Apr 29 2019 21:08:35
%S 1,1,5,47
%N Number of twisted permutations of the nonnegative integers in base 2*n+1 with an adjacency diagram as defined by Knuth in A220952.
%C The concept of the adjacency diagram in A220952 is not limited to base 5, but can be investigated for all odd bases. In "base 1", the path consists of a single node (1,1). For base 3, there is the ternary Gray code A128173 only. A corresponding simple up-down pattern with a path (0,0), ... (0,n), (1,n), ... (1,0), (2,0), ... (n,n) can be constructed for any odd base.
%C Conjecture: a(4) = 673.
%H Georg Fischer, <a href="https://github.com/gfis/fasces">Repository of programs for related sequences</a>, (<a href="https://github.com/gfis/fasces/blob/master/data/gen_paths.pl">gen_paths.pl</a>)
%o (Perl) cf. link
%Y Cf. A128173 (base 3, "n"), A220952 (Knuth, base 5, "Hn"), A307403 ("Hs"), A307404 ("Ln"), A307405 ("Ls"), A300857 (base 7).
%K nonn,hard,more
%O 0,3
%A _Georg Fischer_, Apr 07 2019