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A239774
Number of pairs of functions f, g from a size n set into itself satisfying f(f(g(x))) = f(f(f(x))).
0
1, 1, 10, 285, 14176, 1034145, 105764256, 14367333421
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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$2);
add(add(`if`([seq(evalb(f[f[g[i]]]=f[f[f[i]]]),
i=1..n)]=[true$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:
A231793
A213403
A077281
*
A360341
A049387
A222672
Adjacent sequences:
A239771
A239772
A239773
*
A239775
A239776
A239777
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 April 25 06:14 EDT 2024. Contains 371964 sequences. (Running on oeis4.)