666 is a mathematically interesting number.
It is equal to 2·32·37
666=1+2+3+4+....+34+35+36 and is thus the 36th triangular number and thus the number of objetcts in a triangle 36 objects on a side.
It is equal to the sum of the squares of the first 11 prime numbers: 22 + 32 + 52 + 72 + 112 + 132 + 172 = 666
It is the sum of all roman numerals under 1000: DCLXVI = 500 + 100 + 50 + 10 + 5 + 1 = 666
Because of some rather shaky numerology, many Christian denominations and sects consider it to be the number of the devil, which is why some people are really afraid of it.
Old 666 was a B-17 bomber in the Pacific theater in World War II with the tail number 12666. Until 1943, it had a reputation as a cursed plane that took heavy damage on every flight, and it was being canibalized for parts at the Port Moresby airfield. Jay Zeamer, a pilot with a degree in civil engineering from MIT, who had been unable to find an aircraft for his own, aquired the aircraft and fixed it to flying condition, plus adding improvements like increasing the number of defensive guns from 13 to 19, replacing all .30 caliber guns with .50 caliber, adding a gun for the pilot, and even leaving extra machine guns inside the aircraft to replace any guns that malfucntioned in flight. These improvements made it the most heavily armed plane in the entire Pacific.
On one flight, they shot out searchlights with their guns; on another, they skip-bombed a Japanese carrier. On June 16, 1943, the Old 666 went on an incredible mission: an unescorted 1200-mile-round-trip recon mission. Even while being attacked by 17 Japanese fighters, they completed their mission and shot down at least 3 of the attackers. The bomber was shot up and almost the entire crew was injured, but they completed their mission and made an emergency landing on a friendly airfield. Zeamer, who barely survived, and bombardier Joseph Sarnoski, who shot down an attacker after being fatally wounded, received Metals of Honor, and the rest of the crew received the Distinguished Flying Cross.