309

309 = 3 x 103.

309 is a centered hendecagonal number.

309 is the smallest number whose fifth power (309⁵ = 2817036000549) is pandigital (contains every digit from 0 to 9 at least once).

309³ + 309⁰ + 309⁹ is a prime, with prime digital length.

309 is 373 in base 9. It is 621 in base 7 and 261 in base 11.

309 is a telephone area code serving the state of Illinois.

Source: Number Gossip

606

606 = 2 x 3 x 101.

606 is both a 11-gonal (hendecagonal) number and a centered 11-gonal (hendecagonal) number.

606 is 4411 in base 5.

606 is the sum of six consecutive primes: 606 = 89 + 97 + 101 + 103 + 107 + 109.

606 is the telephone area code the covers the eastern part of the state of Kentucky.

Source: What's Special About This Number?