111111

111111 = 3 x 7 x 11 x 13 x 37.

111111 is a divisor of 100³ - 1.

111111 has the representation 2² x 3⁴ x 7³ - 21.

The 111,111th triangular number is palindromic: 6,172,882,716. The 1111th triangular number (617,716) and the 11th triangular number (66) are also palindromic.

111111 x 111111 = 12345654321.

1 x 9 + 2 = 11

12 x 9 + 3 = 111

123 x 9 + 4 = 1111

1234 x 9 + 5 = 11111

12345 x 9 + 6 = 111111

3 x 37 = 111

33 x 3367 = 111111

3333 x 33336667 = 111111111111

Source: Prime Curios!