673 is the second prime to divide more than one number of the form p# - 1 (673 divides both 149# - 1 and 193# - 1).
673 divides 3333333331. It is the second number of the form (3)w1 to be found composite after many mathematicians thought all numbers of that form were prime.
The Louvre Pyramid is made up of 673 glass lozenges and triangles, not counting the doors.
Chlorophyll a fluoresces at 673 nanometers.
The smallest prime adjacent to any 3-perfect number. [Loungrides]
673 = 1(mod 6) = 1(mod 7)= 1(mod3). [Bergot]
There are 673 numbers N with no two same digits, having the
property that when the sum of the k leftmost digits of N is
divided by k the result is always an integer. [Post and
(There is one curio for this number that has not yet been approved by an editor.)