Search: id:A145845
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%I A145845
%S A145845 1,2,7,34,208,1504,12283,109778,1050820,10614856,111978128
%N A145845 Number of permutations of length 2n+1 which are invariant under the reverse-complement 
               map and have no decreasing subsequences of length 5.
%F A145845 a(n) = sum(j=0, n, C(n,j)^2 * A005802(j))
%F A145845 = sum(j=0, n, C(n,j)^2 * (1/((j+1)^2 (j+2))) *
%F A145845 sum(i=0, j, C(2i,i)*C(j+1,i+i)*C(j+2,i+1)))
%F A145845 where C(n,j) = n!/(j!(n-j)!)
%t A145845 Table[Sum[ Binomial[n, j]^2*(1/((j + 1)^2*(j + 2)))* Sum[Binomial[2*i, 
               i]*Binomial[j + 1, i + 1]* Binomial[j + 2, i + 1], {i, 0, j}], {j, 
               0, n}], {n, 0, 20}]
%Y A145845 Sequence in context: A075834 A011800 A112916 this_sequence A002720 A111539 
               A074059
%Y A145845 Adjacent sequences: A145842 A145843 A145844 this_sequence A145846 A145847 
               A145848
%K A145845 nonn
%O A145845 0,2
%A A145845 Eric Egge (eegge(AT)carleton.edu), Oct 21 2008

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