%I A061552
%S A061552 1,1,2,6,23,103,513,2762,15793,94776,591950,3824112,25431452,173453058,
%T A061552 1209639642,8604450011,62300851632,458374397312,3421888118907,
%U A061552 25887131596018,198244731603623,1535346218316422,12015325816028313
%N A061552 Number of 1324-avoiding permutations of length n.
%D A061552 M. H. Albert, M. Elder, A. Rechnitzer, P. Westcott, M. Zabrocki, On the 
               Wilf-Stanley limit of 4231-avoiding permutations and a conjecture 
               of Arratia, arXiv:math.CO/0502504.
%e A061552 a(4)=23 because all 24 permutations of length 4, except 1324 itself, 
               avoid pattern 1324.
%p A061552 count1324 := proc(n::nonnegint) if (n<4) then return n!; fi; if (n=4) 
               then return 23; fi; return nodes([5,5,5,5], n-5) + nodes([5,3,5,5], 
               n-5) + nodes([5,4,4,5], n-5) + nodes([5,5,4,5], n-5) + nodes([4,3,
               4], n-5) + nodes([5,3,4,5], n-5); end:
%p A061552 nodes := proc(p, h) option remember; local i, j, s, l; if (h=0) then 
               return convert(p, `+`); fi; s := 0; for j to nops(p) do l := p[j]+1; 
               for i from 2 to j do l := l, `min`(j+1, p[i]); od; for i from j+1 
               to p[j] do l := l, p[i-1]+1; od; s := s+nodes([l], h-1); od; return 
               s; end:
%Y A061552 Sequence in context: A004040 A022558 A005802 this_sequence A053488 A117106 
               A137534
%Y A061552 Adjacent sequences: A061549 A061550 A061551 this_sequence A061553 A061554 
               A061555
%K A061552 nonn
%O A061552 0,3
%A A061552 Darko Marinov (marinov(AT)lcs.mit.edu), May 17 2001
%E A061552 More terms from Vince Vatter (vatter(AT)math.rutgers.edu), Feb 26 2005