Logic Masters Deutschland e.V.

Normal sudoku rules apply.
Each row, column and 3x3 box contains the digits 1 to 9.

Standard little killer clues apply.
The numbers outside the grid show the sum of the indicated diagonal. Digits might repeat along the diagonal if allowed by the other rules.

Odd digit.
The grey circle indicate an odd digit.

Loop.
All the even digits outside the central box form a loop. The loop has no branches, and it does not touch itself, even not diagonally. The even digits in the central box might touch the loop.

Try the puzzle on F-Puzzles.
(OBS: F-puzzles do not test/check for the loop.)