Puzzle I cant solve

This was given to me by a teacher from U.S government

Obvious start with 1,2,3
Naturally led among 2,4,1
Eventually they go 4,5,1
An obvious repeat says 6,3,3
To bring to close go 3,5,5
Ending curves with 4,2,2

He then gave us a hint of 1,8

Help.