Logic Masters Deutschland e.V.

Thanks to Scojo for the inspiration for this puzzle! as this puzzle was set for their weekly prompt featuring indexing.
Happy solving!

Rules:

Normal sudoku rules apply. Place the digits 1 to 9 in each Row, Column, and 3X3 box.

159: Digits in column 1 indicate the column in which the digit 1 appears in that row (e.g. if R2C1 is a 4, R2C4 is a 1). The same applies to columns 5 and 9, with the digits 5 and 9 respectively.

Every clue number outside the grid appears exactly twice, One appearance is a Sandwich sum clue and the other is an X-sums clue. It is up to the solver to determine the nature of each clue.

Sandwich clues outside the grid indicate the sum of the digits between 1 and 9 in that row/column.

X-Sums clues outside the grid give the sum of the first X digits in their respective row or column, where X is the digit nearest the clue.

Solve online: SudokuPad