Logic Masters Deutschland e.V.

S-cell chaos construction: divide the grid into regions of 5 orthogonally connected cells. Each row, column, and region must contain the digits 0 to 5 once each. To allow this, place one S-cell that contains 2 digits in each row, column, and region. S-cells may not contain a 0.

Friendly numbered regions: the digit in the top-left cell of a region is its region number and all region numbers are different. Region numbers must equal their row or column number, i.e. they are friendly. Each region number indicates the row of the region number cell in the next column (e.g. if there is a region number at R2C1 that is a 4, then there is a region number at R4C2). S-cells may contain region numbers. The region number in the last column does not need to index the first column.

The region number indexing was inspired by VikingPrime's awesome stadiometer series.

F-Puzzles: https://f-puzzles.com/?id=2d2uzlpd

SudokuPad: https://tinyurl.com/friendlynumberedregionssudoku