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A134243
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Denominators of certain constants c_n = A180609(n)/n! related to Hurwitz numbers.
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2
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1, 2, 2, 3, 12, 4, 6, 4, 12, 6, 15, 60, 120, 60, 20, 60, 3, 5, 60, 120, 8, 1260, 2520, 168, 56, 168, 168, 840, 84, 840, 21, 140, 420, 630, 120, 280, 420, 840, 504, 2520, 840, 840, 315, 2520, 2520, 315, 84, 90, 30, 180, 360, 120, 120, 210, 24, 495, 1980, 2640, 55440, 315, 55440, 45, 2772, 6930, 27720, 9240, 770, 1848, 27720, 27720
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OFFSET
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1,2
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COMMENTS
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Manetti-Ricciardi refer to the c_n as Koszul numbers.
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LINKS
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FORMULA
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Manetti-Ricciardi Theorem 4.4 give a recurrence for the c_n in terms of Stirling numbers.
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EXAMPLE
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The fractions are 1, -1/2, 1/2, -2/3, 11/12, -3/4, -11/6, 29/4, 493/12, -2711/6, -12406/15, 2636317/60, -10597579/120, -439018457/60, 1165403153/20, 118734633647/60, ...
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MATHEMATICA
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K[1] = 1;
K[n_] := K[n] = -2/((n+2)(n-1)) Sum[StirlingS2[n+1, i] K[i], {i, 1, n-1}];
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CROSSREFS
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KEYWORD
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nonn,frac
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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