262

262 = 2 x 131. It is the product of two distinct Sophie Germain primes.

262 is a meandric number: the number of ways a river can cross a road n times.

The sum of the fourth powers of the prime factors of 262 is a prime: 2⁴ + 131⁴ = 294499937, a prime.

The concatenation of the proper divisors (excluding 1 and the number itself) of 262 is a prime: 2131 .

The Messerschmitt Me 262 was the world's first operational jet-powered fighter aircraft.

Source: Wikipedia

55

55 = 5 x 11.

55 is the tenth Fibonacci number.

55 is the tenth triangular number.

55 is a pyramidal number, the sum of the first five square numbers: 55 = 1² + 2² + 3² + 4² + 5².

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

An emerald anniversary celebrates 55 years.

Source: Phillips, R. 2004. Numbers: Facts, Figures and Fiction. Badsey Publications.

140

140 = 2² x 5 x 7.

140 has a unique representation as a sum of three squares: 140 = 2² + 6² + 10².

140 is a square pyramidal number. It is the sum of the first seven squares: 140 = 1² + 2² + 3² + 4² + 5² + 6² + 7².

140 is a harmonic divisor number.

140 Siwa is a large, dark asteroid discovered in 1874.

Source: Prime Curios!

434

434 = 2 x 7 x 31.

434 is a palindrome that produces a composed prime: 4² + 3⁷ + 4³¹ = 4611686018427390107, a prime.

434 is the smallest composite number that satisfies the equation sigma(n + 2) = sigma(n) + 2, where sigma(n) is the sum of the divisors of n.

434 is 2002 in base 6.

434 Hungaria is an asteroid discovered in 1898.

Source: Prime Curios!

859

859 is a prime number.

857 and 859 form a twin prime pair.

859 is the largest prime that cannot be the central number in a 3-by-3 magic square.

859 is the sum of nine positive fifth powers: 859 = 1⁵ + 1⁵ + 2⁵ + 2⁵ + 2⁵ + 2⁵ + 3⁵ + 3⁵ + 3⁵.

859 Bouzar

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ah is an asteroid discovered in 1916.

Source: Prime Curios!

217

217 = 7 x 31.

217 is the ninth centered hexagonal (hex) number.

47 and 89 are primes, as is their concatenation: 4789. Inserting 0 between them transforms the prime into a power: 47089 = 217².

217 is 1001 in base 6 and 161 in base 12.

217 is the telephone area code covering much of central Illinois.

Source: Prime Curios!

64

64 = 2⁶.

64 is the first number after 1 to be both a square and a cube: 64 = 8² = 4³.

64 is the number of integer partitions of 20 into distinct parts.

64 is 121 in base 7 and 44 in base 15. It is 1000000 in base 2, 1000 in base 4, 100 in base 8, 40 in base 16, and 20 in base 32.

The Commodore 64 was an 8-bit home computer introduced in 1982.

Source: Phillips, R. 1994. Number Facts, Figures and Fiction. Cambridge University Press.