A216042 Numbers k such that Sum_{j=1..k-1} (2*j)!/4^j is an integer.

1, 3, 53, 106, 427, 3416, 6806, 13665, 27330, 130030, 220227, 437666

Offset: 1

Author

Vaclav Kotesovec, Aug 30 2012

Keywords

• nonn
• more

Comments

Next term > 1900000.

Crossrefs

Cf. A215972, A216043, A216044, A216045.

Programs

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