189

189 = 3³ x 7.

The product of the four primes in a prime quadruplet (except for 5, 7, 11, 13) always ends in 189. Example: 101 x 103 x 107 x 109 = 121,330,189.

189 is a heptagonal number. It is also a centered cube number.

189 is 10111101 in base 2 (binary). It is 99 in base 20 and 90 in base 21.

189 is a divisor of 55² - 1.

The 189th century will be the first to contain as few as five prime years: 18803, 18839, 18859, 18869, and 18899.

Source: Prime Curios!