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A216045 Numbers k such that Sum_{j=1..k-1} (4j)!/5^j is an integer. 5

%I #12 Feb 14 2021 15:19:45

%S 1,6,30,145,151,592,732,3895,87806,292432

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

%C Next term is > 1500000.

%t seq={}; sum=0; fak=1; k=0; While[k<10000, sum+=fak; If[Denominator[sum]==1, AppendTo[seq,k+1]]; k++; fak*=4*k*(4*k-1)*(4*k-2)*(4*k-3)/5;]; seq

%Y Cf. A215972, A216042, A216043, A216044.

%K nonn,more

%O 1,2

%A _Vaclav Kotesovec_, Aug 30 2012

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Last modified February 25 19:10 EST 2024. Contains 370332 sequences. (Running on oeis4.)