If the side of the triangle is ' S ', then . . .
-- Base of the triangle = S
-- Height of the triangle = 1/2 S √3
-- Area = 1/2 (base) (height) = (S² √3) / 4
-- Perimeter = 3 S
Area / Perimeter (numerical) = [ (S² √3) / 4 ] / 3 S
That ugly thing becomes S √3 / 12 .