Logic Masters Deutschland e.V.

The Rules:

1. Normal sudoku rules apply.
2. [Sandwich] Numbers outside the grid - many of which need to be deduced are the sum of the digits sandwiched between the 1 and the 9 in that row or column.
3. [Outside clues] The digits in the numbers outside of the grid must also be placed in the first three cells from the direction of the clue. For example, in row 3, the 2 and 8 must be placed somewhere in R3C1, R3C2 or R3C3.
4. The clues marked odd or even must be odd or even numbers that satisfy both the sandwich constraint and the outside clues constraint. The ? can be any one or two digit number that satisfies both constraints. A clue like 11, 22, or 33 could be possible if a 1, 2, or 3 appears in the first three cells.

The Puzzle:

Try it on Sven's Sudokupad (with solution)