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%I M2032 N0804 #20 Nov 08 2014 14:49:41
%S 0,0,0,1,2,12,71,481,3708,32028,306723,3228804,37080394,461569226,
%T 6192527700,89102492915,1369014167140,22373840093040,387602212164321,
%U 7095737193164187,136885937242792752,2775675888994318366
%N Number of permutations of length n with two 3-sequences.
%D D. M. Jackson, J. W. Reilly, Permutations with a prescribed number of $p$-runs. Ars Combinatoria 1 (1976), no. 1, 297-305.
%D N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H J. Riordan, <a href="http://projecteuclid.org/euclid.bams/1183507357">Permutations without 3-sequences</a>, Bull. Amer. Math. Soc., 51 (1945), 745-748.
%o (PARI) concat([0,0,0],Vec(sum(m=0,100,((m+2)*(m+1)*(m+2)!/2*(x^6*(1-x)^4/(1-x^3)^4)+(m+1)*(m+1)!*(x^4*(1+x)*(1-x)^3)/(1-x^3)^3)*((x-x^3)/(1-x^3))^m)+O(x^100))) \\ _Tani Akinari_, Nov 08 2014
%Y Cf. A047921.
%K nonn
%O 1,5
%A _N. J. A. Sloane_
%E More terms from _Max Alekseyev_, Feb 20 2010
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