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A239772
Number of pairs of functions f, g from a size n set into itself satisfying f(f(x)) = f(g(f(x))).
0
1, 1, 10, 231, 9688, 603445, 52284816, 5951141035
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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) local l; l:= s(n$2);
add(add(`if`([seq(evalb(f[f[i]]=f[g[f[i]]]),
i=1..n)]=[true$n], 1, 0), g=l), f=l)
end:
seq(a(n), n=0..5); #
Alois P. Heinz
, Jul 16 2014
CROSSREFS
Cf.
A181162
,
A239769
,
A239773
.
Sequence in context:
A027952
A056602
A349731
*
A239773
A087434
A297648
Adjacent sequences:
A239769
A239770
A239771
*
A239773
A239774
A239775
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 May 21 16:27 EDT 2024. Contains 372738 sequences. (Running on oeis4.)