37- is the only two digit number (in base 10) with the following property:
The difference between the two digits (absolute value) equals the square root of the difference between the original number and the least common multiple of the two digits.
7-3=4
4squared = 16
7 x 3 = 21 (least common multiple)
37 – 21 = 16
square root of 16 = 4!