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 A239780 Number of pairs of functions f, g on a size n set into itself satisfying f(f(g(x))) = f(g(g(x))). 0
 1, 1, 12, 279, 11128, 669605, 55937376, 6146973259 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Table of n, a(n) for n=0..7. MAPLE s:= proc(n, i) option remember; `if`(i=0, [[]], map(x-> seq([j, x[]], j=1..n), s(n, i-1))) end: a:= proc(n) (l-> add(add(`if`([true\$n]=[seq(evalb( f[f[g[i]]]=f[g[g[i]]]), i=1..n)], 1, 0), g=l), f=l))(s(n\$2)) end: seq(a(n), n=0..5); # Alois P. Heinz, Jul 17 2014 CROSSREFS Cf. A181162, A239769, A239773. Sequence in context: A220383 A296383 A296640 * A351765 A295037 A295528 Adjacent sequences: A239777 A239778 A239779 * A239781 A239782 A239783 KEYWORD nonn,more AUTHOR Chad Brewbaker, Mar 26 2014 EXTENSIONS a(6)-a(7) from Giovanni Resta, Mar 28 2014 STATUS approved

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Last modified September 24 22:14 EDT 2023. Contains 365582 sequences. (Running on oeis4.)