What is unique about the number 4?

Sham S. Misri

i)                    It is the only number which is spelled with the same number of letters as its numerical value.

                                                F-O-U-R

ii)                  To the nearest one, four is the average temperature of the oceans in degrees Celsius.

iii)                 Water has the maximum density at 4⁰ Centigrade.