640657815 has 32 divisors (see below), whose sum is σ = 1176784896. Its totient is φ = 291548160.

The previous prime is 640657783. The next prime is 640657859. The reversal of 640657815 is 518756046.

It is not a de Polignac number, because 640657815 - 2⁵ = 640657783 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 9735 + ... + 37095.

It is an arithmetic number, because the mean of its divisors is an integer number (36774528).

Almost surely, 2^640657815 is an apocalyptic number.

640657815 is a deficient number, since it is larger than the sum of its proper divisors (536127081).

640657815 is a wasteful number, since it uses less digits than its factorization.

640657815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27599.

The product of its (nonzero) digits is 201600, while the sum is 42.

The square root of 640657815 is about 25311.2191527789. The cubic root of 640657815 is about 862.0690289662.

The spelling of 640657815 in words is "six hundred forty million, six hundred fifty-seven thousand, eight hundred fifteen".