644

644 = 2² x 7 x 23.

644 is a Perrin number.

644 is 212212 in base 3 and 2552 in base 6.

644 is a number made up of only semiprime digits (4, 6, and 9).

644 is the sum of five fourth powers: 644 = 5⁴ + 2⁴ + 1⁴ + 1⁴ + 1⁴.

The USS Lewis and Clark (SSBN-644) was a ballistic missile submarine in the U.S. Navy.

Source: What's Special About This Number?

486

486 = 2 x 3⁵.

486 is a Perrin number.

486 is 200000 in base 3 and 600 in base 9. It is 123 in base 21.

486 is a number with 12 divisors.

486 is the sum of two positive fifth powers: 486 = 3⁵ + 3⁵.

Intel's 486 (short for 80486) microprocessor chip powered many microcomputers, starting in 1986.

Source: What's Special About This Number?