Logic Masters Deutschland e.V.

In addition to standard Sudoku rules:

If a cell contains N, it must be horizontally adjacent to a cell containing 2*N, and vertically adjacent to a cell containing 5*N (whenever those are valid digits). Adjacency wraps around the edges of the board.

Links: F-puzzles, Sudoku Exchange

(Note: This puzzle has two redundant clues! Only the 7 and 6 are necessary for a unique solution.)

Once you notice a property that's a consequence of the rules, the puzzle is pretty easy. This property also helps with a previous puzzle.