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A159716
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Number of permutations of 2 indistinguishable copies of 1..n arranged in a circle with exactly 2 local maxima.
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11
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2, 66, 1168, 16220, 202416, 2395540, 27517568, 310123764, 3447919120, 37934904788, 413863668480, 4483624403284, 48285543009872, 517346347249140, 5518365322864384, 58632646191319220, 620816303380261392, 6553061146974071956, 68979591578665208960, 724285713430953995412
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OFFSET
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2,1
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LINKS
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FORMULA
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a(n) = n*(169*10^(n-2) + 48*3^(n-2) - 84*n*3^(n-2))/49. - Andrew Howroyd, May 10 2020
G.f.: 2*x*(1 + 3*x)*(1 + x - 69*x^2 + 45*x^3) / ((1 - 3*x)^3*(1 - 10*x)^2).
a(n) = 29*a(n-1) - 307*a(n-2) + 1467*a(n-3) - 3240*a(n-4) + 2700*a(n-5) for n>6.
(End)
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PROG
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(PARI) a(n) = {n*(169*10^(n-2) + 48*3^(n-2) - 84*n*3^(n-2))/49} \\ Andrew Howroyd, May 10 2020
(PARI) Vec(2*x*(1 + 3*x)*(1 + x - 69*x^2 + 45*x^3) / ((1 - 3*x)^3*(1 - 10*x)^2) + O(x^20)) \\ Colin Barker, May 19 2020
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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