Let 1st digit = x and 2nd digit = y then 3rd digit = x+y and 4th digit = x+2y and 5th digit = 2x+3y No digit can be 0, since if x or y were 0, then x=y, which is not allowed, If x=1, 1st digit = 1 2nd digit = y 3rd digit = 1+y 4th digit = 1+2y 5th digit = 2+3y The 5th digit must be less than 10, so 2+3y < 10 3y < 8 y < 2 2/3, and it can't be 1, so y must be 2 so 1st digit = 1 2nd digit = 2 3rd digit = 3 4th digit = 5 5th digit = 8 So the first addy number is 12358 ---- If x=2, 1st digit = 2 2nd digit = y 3rd digit = 2+y 4th digit = 2+2y 5th digit = 4+3y The 5th digit must be less than 10, so 4+3y < 10 3y < 6 y < 2 so y must be 1 so 1st digit = 2 2nd digit = 1 3rd digit = 3 4th digit = 4 5th digit = 7 So the second addy number is 12358 ------------------ If x=3, 1st digit = 3 2nd digit = y 3rd digit = 3+y 4th digit = 3+2y 5th digit = 6+3y The 5th digit must be less than 10, so 6+3y < 10 3y < 4 y < 1 1/3 so y must be 1 so 1st digit = 3 2nd digit = 1 3rd digit = 4 4th digit = 5 5th digit = 9 So the third addy number is 31459 ------ We have them all, because if x=4, the 5th digit, 2x+3y, would be at least 11, since y cannot be 0, and 11 is not a digit. So there are only 3 addy numbers: 12358 21347 31459 Edwin