Here is the letter wriggler’s solution:
1] can only be 4 & 1 or 8 & 2 must be 8-2 because b] 4 is between, not at edge.
2] the 9 must be above the 8 (not the centre – the 2 blocks it) making Top Left 5
3] out of the 9 digits only 2, 3 and 1<see d] satisfies this, 2 is already placed
4] 9 is placed so 9, 4 and 3
5] check for no double primes – ok
Arrange the numbers 1 through 9 in the grid so that all of the conditions in the puzzle are satisfied. Every number is used once. The rules are
- The number in the lower left corner is 4 times the number in the upper right corner.
- The 9 is between the 5 and the 8. (on a straight line)
- There is a column in which the sum is equal to the product.
- The 4 is between the 9 and the 3. (on a straight line)
- No prime number is immediately to the left of a prime number.