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%I
%S 1,1,2,6,24,120,720,5020,39790,352470,3445032,36775404,425282892,
%T 5292245764,70471602994,999394962306,15032677450752,238984379214960,
%U 4002966472631160,70448661940661068,1299478739106621670,25067231918730741438,504674373639695198712,10584965637367018566180
%N Number of permutations of [n] that avoid the shuffle pattern s-k-t, where s = 123 and t = 123.
%H Sergey Kitaev, <a href="http://dx.doi.org/10.1016/j.disc.2004.03.017">Partially Ordered Generalized Patterns</a>, Discrete Math. 298 (2005), no. 1-3, 212-229.
%F Let b(n) = A049774(n) = number of permutations avoiding a consecutive 123 pattern. Then a(n) = Sum_{i = 0..n-1} binomial(n-1,i) (2*b(i)*a(n-1-i) - b(i)*b(n-1-i)) for n >= 1 with a(0) = b(0) = 1. [See the recurrence for C_n on p. 220 of Kitaev (2005).] - _Petros Hadjicostas_, Oct 30 2019
%Y Cf. A000142, A049774.
%K nonn
%O 0,3
%A _N. J. A. Sloane_, Feb 16 2019
%E More terms from _Petros Hadjicostas_, Oct 31 2019
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