333667

This number is a prime.

The only prime with period length 9. Note that it is the largest prime factor of the palindrome 12345678987654321.

When any three-digit number is multiplied by 333667 and the number three, the result will always be the same three digits repeated three times. E.g., 123 x 333667 x 3 = 123123123. Any nine-digit number that repeats three digits three times will always have 333667 as a highest prime factor. [Schuler]

The greatest prime factor of any 9-digit repdigit is 333667. [La Haye]

The 333rd hexagon number. This means 333667 coins could form a hexagon shape with one coin in the middle and 333 + 1 coins on each side. [Schuler]

333667 is the smallest emirp formed from the concatenation in order of two 3-digit composite numbers summed to a thousand (333, 667). [Loungrides]