A216149 Numbers k such that Sum_{j=1..k-1} (3*j)!/5^j is an integer.

1, 3, 16

Offset: 1

Author

Vaclav Kotesovec, Sep 02 2012

Keywords

• nonn
• more
• bref

Comments

The next term, if it exists, is greater than 1000000. - Vaclav Kotesovec, Sep 11 2012

Crossrefs

Cf. A215972, A216042, 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*=3*k*(3*k-1)*(3*k-2)/5;]; seq
Select[Range[20],IntegerQ[Sum[(3k)!/5^k,{k,#-1}]]&] (* Harvey P. Dale, Apr 07 2019 *)