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%I #5 Jan 26 2017 15:08:32
%S 0,0,1,6,55,660,9751,170898,3463615,79669320,2050086511,58346365110,
%T 1819621847407,61705703989020,2260586259354151,88971796139662842,
%U 3743940350046570751,167735288431662235920,7971302827015366403551,400510700317394780627934,21212944650652080893863087
%N a(n) = ((n-2)^n - 2*(n-1)^n + n^n)/2.
%F a(n) ~ n^n*(1/2+(1/2-1/n)*e^(-2)+(1/(2*n)-1)*e^(-1)).
%p a := n -> ((n-2)^n-2*(n-1)^n+n^n)/2:
%p seq(a(n), n=0..21);
%Y Cf. A000312, A045531, A281595.
%K nonn
%O 0,4
%A _Peter Luschny_, Jan 26 2017
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