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A066830
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a(n) = lcm(n+1, n-1).
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8
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0, 3, 4, 15, 12, 35, 24, 63, 40, 99, 60, 143, 84, 195, 112, 255, 144, 323, 180, 399, 220, 483, 264, 575, 312, 675, 364, 783, 420, 899, 480, 1023, 544, 1155, 612, 1295, 684, 1443, 760, 1599, 840, 1763, 924, 1935, 1012, 2115, 1104, 2303, 1200, 2499, 1300
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OFFSET
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1,2
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COMMENTS
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a(n+2) is the order of rowmotion on a poset obtained by adjoining a unique minimal and maximal element to a disjoint union of at least two chains of n elements. - Nick Mayers, Jun 01 2018
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LINKS
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FORMULA
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a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6) for n > 6.
a(n) = (3+(-1)^n)*(-1+n^2)/4.
G.f.: x^2*(x^4 - 6*x^2 - 4*x - 3) / ((x-1)^3*(x+1)^3).
(End)
a(n) = numerator((n^2 - 1)/2).
Sum_{n>=2} 1/a(n) = 1. (End)
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MAPLE
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MATHEMATICA
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Table[LCM[n-1, n+1], {n, 100}] (* Zak Seidov, Oct 23 2009 *)
a[n_] := If[EvenQ[n], n(n+2)/2, n(n+2)]; Table[a[n], {n, 0, 50}] (* Jean-François Alcover, Jun 13 2017 *)
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PROG
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(PARI) { for (n=1, 1000, write("b066830.txt", n, " ", lcm(n+1, n-1)) ) } \\ Harry J. Smith, Mar 30 2010
(PARI) concat(0, Vec(x^2*(x^4-6*x^2-4*x-3)/((x-1)^3*(x+1)^3) + O(x^100))) \\ Colin Barker, Nov 05 2014
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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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STATUS
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approved
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