Digits surrounding a circle must sum to the number in the circle. Digits may not repeat around a circle.
Empty circles all represent the same sum, which the solver must find.
Normal Sudoku rules apply.
Try it at F-Puzzles.
Solution code: Digits from last (9:th) column, top to bottom.
on 16. December 2022, 15:34 by chain.reader
That was quite interesting.
I went with a pencilmark heavy approach... The solution emerged on it's own, bit by bit.