← Complete problem index

PROJECT EULER · #0672

One More One

Statement only · UnsolvedOriginal problem ↗

Consider the following process that can be applied recursively to any positive integer n:

  • if n=1 do nothing and the process stops,
  • if n is divisible by 7 divide it by 7,
  • otherwise add 1.

Define g(n) to be the number of 1's that must be added before the process ends. For example:

125+1126÷718+119+120+121÷73+14+15+16+17÷71.

Eight 1's are added so g(125)=8. Similarly g(1000)=9 and g(10000)=21.

Define S(N)=n=1Ng(n) and H(K)=S(7K111). You are given H(10)=690409338.

Find H(109) modulo 1117117717.

Write-up coming later

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