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%I #16 Oct 31 2019 01:29:24
%S 1,1,2,6,24,120,710,4815,36650,308778,2850294,28602468,310041806,
%T 3610879857,44975227466,596677473990,8401332033264,125140942951896,
%U 1966223504686334,32501786913873447,563877339150924866,10245134152041643818,194553155073687332550,3854328529787275833204
%N Number of permutations of [n] that avoid the shuffle pattern s-k-t, where s = 12 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) (a(n-1-i) + b(i) * a(n-1-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 30 2019