login
The OEIS is supported by
the many generous donors to the OEIS Foundation
.
Hints
(Greetings from
The On-Line Encyclopedia of Integer Sequences
!)
A239779
Number of pairs of functions f, g, from a size n set into itself satisfying f(g(g(x))) = g(g(f(x))).
0
1, 1, 12, 267, 9088, 425465, 27039096, 2261637637
(
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[g[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:
A068271
A068283
A003390
*
A107485
A293270
A341815
Adjacent sequences:
A239776
A239777
A239778
*
A239780
A239781
A239782
KEYWORD
nonn
,
more
AUTHOR
Chad Brewbaker
, Mar 26 2014
EXTENSIONS
a(6)-a(7) from
Giovanni Resta
, Mar 28 2014
STATUS
approved
Lookup
|
Welcome
|
Wiki
|
Register
|
Music
|
Plot 2
|
Demos
|
Index
|
Browse
|
More
|
WebCam
Contribute new seq. or comment
|
Format
|
Style Sheet
|
Transforms
|
Superseeker
|
Recents
The OEIS Community
| Maintained by
The OEIS Foundation Inc.
License Agreements, Terms of Use, Privacy Policy.
.
Last modified August 21 08:16 EDT 2024. Contains 375345 sequences. (Running on oeis4.)