Given a collection of numbers, the isolated numbers are ones in the collection with no consecutive numbers (on either side.) For example if the numbers are 1,3,4,6,8,9 then the isolated numbers would be 1 and 6 because 3 is next to 4 and 8 is next to 9. (Alternately we could say the isolated numbers are numbers n in the set so that both n+1 and n-1 are not in the set.)
Here is a Sudoku I constructed based around this one idea.
For more information and the solution visit
Quadrata.