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A124236
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a(n) = denominator of (sum{k=1 to n} H(2k)(2k)!/(k!(k+n+1)!) = sum{k=0 to n-1} H(n-k)(2k)!/ (k!(k+n+1)!)), where H(k) = sum{j=1 to k} 1/j (i.e. the k-th harmonic number).
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2
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2, 3, 144, 30240, 4725, 7983360, 108972864000, 8072064000, 453682944000, 403179783552000, 1250891123328000, 179527894020034560000, 42009527200688087040000, 9335450489041797120000
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| R. J. Mathar, Table of n, a(n) for n = 1..30
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MATHEMATICA
| f[n_] := Denominator[Sum[HarmonicNumber[2k]*Factorial[2k]/(Factorial[k]*Factorial[k + n + 1]), {k, n}]]; Table[f[n], {n, 16}] (*Chandler*)
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PROG
| (PARI) H(n)={ if(n==0, 0, sum(k=1, n, 1/k)) ; }
(PARI) A124236(n)={ denominator(sum(k=1, n, H(2*k)*(2*k)!/k!/(k+n+1)!)) ; }
(PARI) A124236alt(n)={ denominator(sum(k=0, n-1, H(n-k)*(2*k)!/k!/(k+n+1)!)) ; } (Mathar)
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CROSSREFS
| Cf. A124235.
Sequence in context: A066908 A057738 A042073 * A042369 A042701 A106715
Adjacent sequences: A124233 A124234 A124235 * A124237 A124238 A124239
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KEYWORD
| frac,nonn
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AUTHOR
| Leroy Quet Oct 22 2006
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EXTENSIONS
| Extended by R. J. Mathar and Ray Chandler (rayjchandler(AT)sbcglobal.net), Oct 23 2006
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