Search: id:A052503
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%I A052503
%S A052503 1,1,9,105,2625,76545,3440745,176080905,12034447425,922995698625,
%T A052503 87505195602825
%N A052503 Number of permutations sigma without fixed point such that sigma^4=Id.
%H A052503 INRIA Algorithms Project, <a href="http://algo.inria.fr/bin/encyclopedia?Search=ECSnb&argsearch=28">
               Encyclopedia of Combinatorial Structures 28</a>
%F A052503 E.g.f.: exp(1/2*x^2+1/4*x^4)
%F A052503 Recurrence: {a(1)=0, a(0)=1, a(2)=1, a(3)=0, (-11*n-6-n^3-6*n^2)*a(n)+(-n-3)*a(n+2)+a(n+4)}
%p A052503 spec := [S,{S=Set(Union(Cycle(Z,card=2),Cycle(Z,card=4)))},labeled]: 
               seq(combstruct[count](spec,size=n), n=0..20);
%Y A052503 Sequence in context: A081461 A110698 A012485 this_sequence A122569 A039619 
               A080505
%Y A052503 Adjacent sequences: A052500 A052501 A052502 this_sequence A052504 A052505 
               A052506
%K A052503 easy,nonn
%O A052503 0,3
%A A052503 encyclopedia(AT)pommard.inria.fr, Jan 25 2000

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