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%I #4 May 15 2013 18:11:50
%S 2,4,8,28,128,748,5168,41068,368048,3669868,40284848,482671468,
%T 6267305648,87660962668,1313941673648,21010450850668,357001369769648,
%U 6423384156578668,122002101778601648,2439325392333218668
%N a(n) = index of first derangement of 1..n (n>=2).
%F a(0)=1, a(1)=2, a(n)=a(n-2)+(n-1)!; a(n)=a(n-1)=abs(A058006(n)).
%e n=2: permutations are
%e per={{1,2},{2,1}},
%e per(2)={2,1} is the first derangement, hence a(2)=2;
%e n=3: permutations are
%e per={{1,2,3},{1,3,2},{2,1,3},{2,3,1},{3,1,2},{3,2,1}},
%e per(3)= {2,1,3} is the first derangement, hence a(3)=2;
%e n=4: permutations are
%e per={{1,2,3,4},{1,2,4,3},{1,3,2,4},{1,3,4,2},{1,4,2,3},{1,4,3,2},{2,1,3,4},{2,1,4,3},{2,3,1,4},{2,3,4,1},{2,4,1,3},{2,4,3,1},{3,1,2,4},{3,1,4,2},{3,2,1,4},{3,2,4,1},{3,4,1,2},{3,4,2,1},{4,1,2,3},{4,1,3,2},{4,2,1,3},{4,2,3,1},{4,3,1,2},{4,3,2,1}},
%e per(8)= {2,1,4,3} is the first derangement, hence a(4)=8.
%t c[0]=1;c[1]=2;c[n_]:=c[n]=c[n-2]+(n-1)!;A1=Table[c[n],{n,2,20}]
%Y Cf. A058006.
%K nonn
%O 2,1
%A _Zak Seidov_, Jan 16 2008
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