640256217 has 8 divisors (see below), whose sum is σ = 854805696. Its totient is φ = 426272112.

The previous prime is 640256207. The next prime is 640256263. The reversal of 640256217 is 712652046.

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

It is not a de Polignac number, because 640256217 - 2⁸ = 640255961 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640256207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 138693 + ... + 143234.

It is an arithmetic number, because the mean of its divisors is an integer number (106850712).

Almost surely, 2^640256217 is an apocalyptic number.

It is an amenable number.

640256217 is a deficient number, since it is larger than the sum of its proper divisors (214549479).

640256217 is a wasteful number, since it uses less digits than its factorization.

640256217 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 282687.

The product of its (nonzero) digits is 20160, while the sum is 33.

The square root of 640256217 is about 25303.2847077212. The cubic root of 640256217 is about 861.8888612516. Note that the first 4 decimals are identical.

The spelling of 640256217 in words is "six hundred forty million, two hundred fifty-six thousand, two hundred seventeen".