A216149 - OEIS

A216149

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

1, 3, 16

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OFFSET

1,2

COMMENTS

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

LINKS

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 *)

CROSSREFS

KEYWORD

nonn,more,bref

AUTHOR

STATUS

approved