640257 has 8 divisors (see below), whose sum is σ = 857376. Its totient is φ = 424992.

The previous prime is 640249. The next prime is 640259. The reversal of 640257 is 752046.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 640257 - 2³ = 640249 is a prime.

640257 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640257.

It is not an unprimeable number, because it can be changed into a prime (640259) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1138 + ... + 1604.

It is an arithmetic number, because the mean of its divisors is an integer number (107172).

2⁶⁴⁰²⁵⁷ is an apocalyptic number.

It is an amenable number.

640257 is a deficient number, since it is larger than the sum of its proper divisors (217119).

640257 is a wasteful number, since it uses less digits than its factorization.

640257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 927.

The product of its (nonzero) digits is 1680, while the sum is 24.

The square root of 640257 is about 800.1606088780. The cubic root of 640257 is about 86.1889212600.

The spelling of 640257 in words is "six hundred forty thousand, two hundred fifty-seven".