|
|
A254570
|
|
The number of unordered pairs (f,g) of functions from {1..n} to itself such that fg=gf (i.e., f(g(i))=g(f(i)) for all i) where f and g are distinct.
|
|
2
|
|
|
0, 3, 57, 1284, 34220, 1098720, 41579328, 1832244288, 92830006368, 5353120671120, 348383876993900, 25409389391925264, 2064511110000765192, 185885772163424273304, 18458953746901624026000, 2012589235930543617012480, 239897773975844015012351360, 31132547318002718989156350240, 4380969784826872849927354999092, 665896601825393760478978112600400
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
The a(2) = 3 pairs of maps [2] -> [2] are:
01: [ 1 1 ] [ 1 2 ]
02: [ 1 2 ] [ 2 1 ]
03: [ 1 2 ] [ 2 2 ]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|