%I #9 Feb 14 2024 14:28:27
%S 1,2,9,48,25,2160,2205,17920,5103,18144000,21175,2874009600,11293425,
%T 100452352,9577693125,167382319104000,253127875,57621363351552000,
%U 282135852999,75676057600000,372075093219375,12364008005553684480000,57618381445625,11912609313278197235712
%N a(n) = numerator((n!)^2/(2*(n-2)!*n^n)).
%C a(n) is the numerator of the probability that a sequence of n integers randomly chosen from [n] contains exactly n - 1 different integers (see Brualdi, pp. 57-58).
%D Richard A. Brualdi, Introductory Combinatorics, 5th ed. Pearson Education Inc., 2009.
%t a[n_]:=Numerator[n!^2/(2(n-2)!n^n)]; Array[a,24,2]
%Y Cf. A000142, A000312, A001044, A370201 (denominators).
%K nonn,frac
%O 2,2
%A _Stefano Spezia_, Feb 11 2024