655

655 = 5 x 131.

655 is a semiprime (product of two prime numbers) that is the product of two Sophie Germain primes, 5 and 131.

655 is a number that cannot be written as a sum of three squares.

655 is a divisor of 61⁵ - 1.

655 is 22033 in base 4 and 10110 in base 5.

Iran Air Flight 655 was an airliner shot down by U.S. missiles in 1988 toward the end of the Iran-Iraq war.

Source: On-Line Encyclopedia of Integer Sequences