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A128492
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Denominator of Sum_{k=1..n} 1/(2*k-1)^2.
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4
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1, 9, 225, 11025, 99225, 12006225, 2029052025, 405810405, 117279207045, 42337793743245, 42337793743245, 22396692890176605, 2799586611272075625, 25196279501448680625, 21190071060718340405625
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OFFSET
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1,2
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COMMENTS
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Old definition was "Denominators of partial sums for a series for (Pi^2)/8".
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LINKS
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FORMULA
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EXAMPLE
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Fractions begin: 1, 10/9, 259/225, 12916/11025, 117469/99225, 14312974/12006225, 2430898831/2029052025, 487983368/405810405, ... = A120268/A128492.
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MATHEMATICA
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a[n_] := Pi^2/8 - PolyGamma[1, n+1/2]/4 // Simplify // Denominator; Table[a[n], {n, 1, 15}] (* Jean-François Alcover, Dec 17 2013 *)
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PROG
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(PARI) a(n) = denominator(sum(k=1, n, 1/(2*k-1)^2)); \\ Michel Marcus, May 09 2020
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CROSSREFS
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KEYWORD
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nonn,frac,easy
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AUTHOR
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EXTENSIONS
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Definition replaced with Lang's formula by Bruno Berselli, Dec 02 2013
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STATUS
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approved
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