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 A185411 A triangular decomposition of the double factorial numbers A001147. 6
 1, 0, 1, 0, 2, 1, 0, 4, 10, 1, 0, 8, 60, 36, 1, 0, 16, 296, 516, 116, 1, 0, 32, 1328, 5168, 3508, 358, 1, 0, 64, 5664, 42960, 64240, 21120, 1086, 1, 0, 128, 23488, 320064, 900560, 660880, 118632, 3272, 1, 0, 256, 95872, 2225728, 10725184, 14713840, 6049744, 638968, 9832, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,5 COMMENTS Row sums are A001147. Reversal of A185410. Contains A156919 as submatrix. Row n counts perfect matchings of [2n] by number of matches in which the smaller entry is odd. For example, T(2,1)=2 counts 13/24, 14/23, in each of which only the first matching pair has an odd smaller entry. Outline proof. Consider the map on perfect matchings of [2n] given by "delete the entries n and n-1 and, if they were not originally matched to each other, match up their now-unmatched partners". Consideration of this map and its effect on the statistic "number of matches in which the smaller entry is odd" yields the Mathematica recurrence below. - David Callan, Dec 13 2011 Triangle T(n,k), 0<=k<=n, given by (0, 2, 0, 4, 0, 6, 0, 8, 0, 10, 0, ...) DELTA (1, 0, 3, 0, 5, 0, 7, 0, 9, 11, 0, ...) where DELTA is the operator defined in A084938. - Philippe Deléham, Feb 12 2013 LINKS G. C. Greubel, Table of n, a(n) for the first 50 rows, flattened Shi-Mei Ma, A family of two-variable derivative polynomials for tangent and secant, arXiv: 1204.4963v3 [math.CO], 2012. Shi-Mei Ma, A family of two-variable derivative polynomials for tangent and secant, Elect. J. Combinat. 20 (1) (2013) #P11. Shi-Mei Ma, T. Mansour, D. Callan, Some combinatorial arrays related to the Lotka-Volterra system, arXiv:1404.0731 [math.CO], 2014. S.-M. Ma, T. Mansour and D. G. L. Wang, Combinatorics of Dumont differential system on the Jacobi elliptic functions, arXiv:1403.0233 [math.CO], 2014. Shi-Mei Ma, Toufik Mansour, David G.L. Wang, Yeong-Nan Yeh, Several variants of the Dumont differential system and permutation statistics, Science China Mathematics 60 (2018). S.-M. Ma, Y.-N. Yeh, Stirling permutations, cycle structures of permutations and perfect matchings, arXiv:1503.06601 [math.CO], 2015. FORMULA G.f.: 1/(1-xy/(1-2x/(1-3xy/(1-4x/(1-5xy/(1-6x/(1-7xy/(1- ... (continued fraction). T(n,k) = (2n-2k+1)*T(n-1,k-1) + 2k*T(n-1,k), T(0,0) = 1, T(n,k) = 0 if k<0 or if k>n. - Philippe Deléham, Feb 12 2013 T(n,k) = 2^(n-k)*A211399(n,k). - Philippe Deléham, Feb 12 2013 EXAMPLE 1, 0,   1, 0,   2,     1, 0,   4,    10,       1, 0,   8,    60,      36,        1, 0,  16,   296,     516,      116,        1, 0,  32,  1328,    5168,     3508,      358,       1, 0,  64,  5664,   42960,    64240,    21120,    1086,      1, 0, 128, 23488,  320064,   900560,   660880,  118632,   3272,    1, 0, 256, 95872, 2225728, 10725184, 14713840, 6049744, 638968, 9832, 1 MATHEMATICA u[n_, 0] := If[n==0, 1, 0];  u[n_, m_] /; m==1 := 2^(n - 1);  u[n_, m_] /; m==n>=1 := 1;  u[n_, m_] /; 1

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Last modified April 22 19:11 EDT 2021. Contains 343177 sequences. (Running on oeis4.)