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A216042 Numbers k such that Sum_{j=1..k-1} (2*j)!/4^j is an integer. 5
1, 3, 53, 106, 427, 3416, 6806, 13665, 27330, 130030, 220227, 437666 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Next term > 1900000.

LINKS

Table of n, a(n) for n=1..12.

MATHEMATICA

seq={}; sum=0; fak=1; k=0; While[k<10000, sum+=fak; If[Denominator[sum]==1, AppendTo[seq, k+1]]; k++; fak*=k*(2k-1)/2; ]; seq

CROSSREFS

Cf. A215972, A216043, A216044, A216045.

Sequence in context: A178608 A106997 A141929 * A292530 A036941 A113612

Adjacent sequences:  A216039 A216040 A216041 * A216043 A216044 A216045

KEYWORD

nonn,more

AUTHOR

Vaclav Kotesovec, Aug 30 2012

STATUS

approved

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Last modified May 20 20:15 EDT 2022. Contains 353876 sequences. (Running on oeis4.)