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A239776
Number of pairs of functions f, g from a size n set into itself satisfying f(f(g(x))) = g(g(f(x))).
0
1, 1, 12, 189, 5200, 208945, 11517936, 828676933
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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]]]=g[g[f[i]]]), i=1..n)], 1, 0), g=l), f=l))(s(n$2))
end:
seq(a(n), n=0..5); #
Alois P. Heinz
, Jul 16 2014
CROSSREFS
Cf.
A181162
,
A239769
,
A239773
.
Sequence in context:
A218886
A239294
A294409
*
A071990
A230757
A196483
Adjacent sequences:
A239773
A239774
A239775
*
A239777
A239778
A239779
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 August 21 11:52 EDT 2024. Contains 375353 sequences. (Running on oeis4.)