I'm trying to solve a 3x3 magic square for 99 which starts at 29. I got the rows, columns and one diagonal but the other diagonal is (way) off.
Is there even a magic square which satisfies both diagonals for these parameters? As you can see I've been playing around in a spreadsheet, moving numbers around. But is there a quicker way to spot if a magic square for a number starting at an arbitrary number is possible?