640247 has 2 divisors, whose sum is σ = 640248. Its totient is φ = 640246.

The previous prime is 640231. The next prime is 640249. The reversal of 640247 is 742046.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 640247 - 2⁴ = 640231 is a prime.

Together with 640249, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is equal to p₅₂₀₉₇ and since 640247 and 52097 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320123 + 320124.

It is an arithmetic number, because the mean of its divisors is an integer number (320124).

2⁶⁴⁰²⁴⁷ is an apocalyptic number.

640247 is a deficient number, since it is larger than the sum of its proper divisors (1).

640247 is an equidigital number, since it uses as much as digits as its factorization.

640247 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1344, while the sum is 23.

The square root of 640247 is about 800.1543601081. The cubic root of 640247 is about 86.1884725372.

The spelling of 640247 in words is "six hundred forty thousand, two hundred forty-seven".