Search: id:A121555
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%I A121555
%S A121555 1,2,7,32,178,1164,8748,74304,704016,7362720,84255840,1047358080,
%T A121555 14054739840,202514376960,3118666924800,51119166873600,888640952371200,
%U A121555 16330301780889600,316322420114534400,6441691128993792000
%N A121555 Number of 1-cell columns in all deco polyominoes of height n. A deco 
               polyomino is a directed column-convex polyomino in which the height, 
               measured along the diagonal, is attained only in the last column.
%C A121555 a(n)=Sum(k*A121554(n,k),k=0..n).
%D A121555 E. Barcucci, A. Del Lungo and R. Pinzani, "Deco" polyominoes, permutations 
               and random generation, Theoretical Computer Science, 159, 1996, 29-42.
%F A121555 a(1)=1, a(n)=n*a(n-1)+(n-2)!*(n-2) for n>=2.
%e A121555 a(2)=2 because the deco polyominoes of height 2 are the vertical and 
               horizontal dominoes, having, respectively, 0 and 2 columns with exactly 
               1 cell.
%p A121555 a[1]:=1: for n from 2 to 23 do a[n]:=n*a[n-1]+(n-2)!*(n-2) od: seq(a[n],
               n=1..23);
%Y A121555 Cf. A121554.
%Y A121555 Sequence in context: A005362 A059439 A006014 this_sequence A097900 A000153 
               A006154
%Y A121555 Adjacent sequences: A121552 A121553 A121554 this_sequence A121556 A121557 
               A121558
%K A121555 nonn
%O A121555 1,2
%A A121555 Emeric Deutsch (deutsch(AT)duke.poly.edu), Aug 08 2006

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