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 A216044 Numbers k such that Sum_{j=1..k-1} (4j)!/16^j is an integer. 5

%I #15 Feb 14 2021 18:34:18

%S 1,3,13,15,61,106,253,27545,62785,218107,1004593

%N Numbers k such that Sum_{j=1..k-1} (4j)!/16^j is an integer.

%C Next term > 1200000.

%t seq={}; sum=0; fak=1; k=0; While[k<10000, sum+=fak; If[Denominator[sum]==1, AppendTo[seq,k+1]]; k++; fak*=k*(4*k-1)*(4*k-2)*(4*k-3)/4;]; seq

%Y Cf. A215972, A216042, A216043, A216045.

%K nonn,more

%O 1,2

%A _Vaclav Kotesovec_, Aug 30 2012

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Last modified December 6 21:43 EST 2023. Contains 367616 sequences. (Running on oeis4.)