cp's OEIS Frontend

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.

%I A254570 #5 Feb 01 2015 15:14:18
%S A254570 0,3,57,1284,34220,1098720,41579328,1832244288,92830006368,
%T A254570 5353120671120,348383876993900,25409389391925264,2064511110000765192,
%U A254570 185885772163424273304,18458953746901624026000,2012589235930543617012480,239897773975844015012351360,31132547318002718989156350240,4380969784826872849927354999092,665896601825393760478978112600400
%N 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.
%F A254570  a(n) = (A181162(n) - n^n)/2.
%e A254570 The a(2) = 3 pairs of maps [2] -> [2] are:
%e A254570 01:  [ 1 1 ]  [ 1 2 ]
%e A254570 02:  [ 1 2 ]  [ 2 1 ]
%e A254570 03:  [ 1 2 ]  [ 2 2 ]
%Y A254570  Cf. A181162 (ordered pairs), A254569 (unordered pairs).
%K A254570 nonn
%O A254570 1,2
%A A254570 _Joerg Arndt_, Feb 01 2015