Mystery Sum Sudoku
Here is the third installment of our series of Sudoku variations. It was kindly provided by Brainfreeze puzzles, a puzzle making company run by the mathematician Laura Taalman and the software developer Philip Riley, whose book Color Sudoku is published by Sterling Publishing.
Fill in the grid so that each row, column, and block contain the numbers 1-9 exactly once, and so that there are no repeated entries in any connected shaded region. In addition, all shaded regions of a given color add to the same sum; for example, if one red shaded region has entries that sum to 21, then all red shaded regions in that puzzle sum to 21. The sums are not given; you must determine them yourself.