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%I #11 Oct 12 2015 18:11:05
%S 1,1,6,24,120,1440,5040,40320,362880,3628800,39916800,479001600,
%T 6227020800,87178291200,1307674368000,20922789888000,355687428096000,
%U 6402373705728000,121645100408832000,2432902008176640000
%N Size of the automorphism group of the symmetric group S_n.
%C For all n except n=2 and n=6, Aut(S_n) is S_n itself, i.e. S_n has no outer automorphisms. Aut(S_2) is trivial and Aut(S_6) is of order 2*|S_6| = 1440 - there is an outer involution.
%F a(n) = n! except for n=2 and 6.
%o (PARI) if(n>6,n!,[1, 1, 6, 24, 120, 1440][n]) \\ _Charles R Greathouse IV_, Oct 12 2015
%Y Cf. A000142.
%K nonn,easy
%O 1,3
%A Ola Veshta (olaveshta(AT)my-deja.com), Mar 22 2001
%E Offset corrected by _Stephen A. Silver_, Feb 09 2013