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

1, 3, 16

Offset

1,2

Comments

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

Links

Table of n, a(n) for n=1..3.

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

Cf. A215972, A216042, A216043, A216044, A216045.

Sequence in context: A134807 A364799 A004002 * A194604 A078355 A107823

Adjacent sequences: A216146 A216147 A216148 * A216150 A216151 A216152

Keyword

nonn,more,bref

Author

Vaclav Kotesovec, Sep 02 2012

Status

approved