Search: id:A033305
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%I A033305
%S A033305 1,0,1,2,4,6,13,24,45,84,160,300,565,1064,2005,3774,7108,
%T A033305 13386,25209,47472,89401,168360,317056,597080,1124425,2117520,
%U A033305 3987721,7509690,14142276,26632782,50154949,94451976,177872293
%N A033305 Number of permutations (p1,...,pn) such that 1<=|pk-k|<=2 for all k.
%D A033305 Lehmer, D. H.; Permutations with strongly restricted displacements. Combinatorial 
               theory and its applications, II (Proc. Colloq., Balatonfured, 1969), 
               pp. 755-770. North-Holland, Amsterdam, 1970.
%D A033305 R. P. Stanley, Enumerative Combinatorics I, p. 252, Example 4.7.16.
%F A033305 G.f.: (1-x)/(1-x-x^2-x^3-x^4+x^5).
%F A033305 a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) - a(n-5)
%Y A033305 Sequence in context: A058598 A087549 A109078 this_sequence A105543 A027712 
               A138307
%Y A033305 Adjacent sequences: A033302 A033303 A033304 this_sequence A033306 A033307 
               A033308
%K A033305 nonn
%O A033305 0,4
%A A033305 N. J. A. Sloane (njas(AT)research.att.com).
%E A033305 New description from Max Alekseyev (maxale(AT)gmail.com), Jul 09 2006

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