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PROJECT EULER · #0511

Sequences with Nice Divisibility Properties

Statement only · UnsolvedOriginal problem ↗

Let Seq(n,k) be the number of positive-integer sequences {ai}1in of length n such that:

  • n is divisible by ai for 1in, and
  • n+a1+a2++an is divisible by k.

Examples:

Seq(3,4)=4, and the 4 sequences are:
{1,1,3}
{1,3,1}
{3,1,1}
{3,3,3}

Seq(4,11)=8, and the 8 sequences are:
{1,1,1,4}
{1,1,4,1}
{1,4,1,1}
{4,1,1,1}
{2,2,2,1}
{2,2,1,2}
{2,1,2,2}
{1,2,2,2}

The last nine digits of Seq(1111,24) are 840643584.

Find the last nine digits of Seq(1234567898765,4321).

Write-up coming later

The complete problem is available here. An approach, code, and answer will be added later.