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A124236 a(n) = denominator of (Sum_{k=1..n} H(2k)(2k)!/(k!(k+n+1)!) = Sum_{k=0..n-1} H(n-k)(2k)!/ (k!(k+n+1)!)), where H(k) = Sum_{j=1..k} 1/j (i.e., the k-th harmonic number). 2
2, 3, 144, 30240, 4725, 7983360, 108972864000, 8072064000, 453682944000, 403179783552000, 1250891123328000, 179527894020034560000, 42009527200688087040000, 9335450489041797120000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

R. J. Mathar, Table of n, a(n) for n = 1..30

MATHEMATICA

f[n_] := Denominator[Sum[HarmonicNumber[2k]*Factorial[2k]/(Factorial[k]*Factorial[k + n + 1]), {k, n}]]; Table[f[n], {n, 16}] (* Ray Chandler, Oct 23 2006 *)

PROG

(PARI) H(n)={ if(n==0, 0, sum(k=1, n, 1/k)) ; }

A124236(n)={ denominator(sum(k=1, n, H(2*k)*(2*k)!/k!/(k+n+1)!)) ; }

A124236alt(n)={ denominator(sum(k=0, n-1, H(n-k)*(2*k)!/k!/(k+n+1)!)) ; } \\ R. J. Mathar, 23 Oct 2006

CROSSREFS

Cf. A124235 (numerators).

Sequence in context: A234999 A254787 A042073 * A115231 A042369 A328257

Adjacent sequences:  A124233 A124234 A124235 * A124237 A124238 A124239

KEYWORD

frac,nonn

AUTHOR

Leroy Quet, Oct 22 2006

EXTENSIONS

Extended by R. J. Mathar and Ray Chandler, Oct 23 2006

STATUS

approved

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Last modified February 25 19:39 EST 2021. Contains 341618 sequences. (Running on oeis4.)