640215871 has 4 divisors (see below), whose sum is σ = 646554744. Its totient is φ = 633877000.

The previous prime is 640215839. The next prime is 640215881. The reversal of 640215871 is 178512046.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 640215871 - 2⁵ = 640215839 is a prime.

It is a super-2 number, since 2×640215871² = 819752722960577282, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640215881) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 3169285 + ... + 3169486.

It is an arithmetic number, because the mean of its divisors is an integer number (161638686).

Almost surely, 2^640215871 is an apocalyptic number.

640215871 is a deficient number, since it is larger than the sum of its proper divisors (6338873).

640215871 is a wasteful number, since it uses less digits than its factorization.

640215871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6338872.

The product of its (nonzero) digits is 13440, while the sum is 34.

The square root of 640215871 is about 25302.4874468895. The cubic root of 640215871 is about 861.8707567816.

The spelling of 640215871 in words is "six hundred forty million, two hundred fifteen thousand, eight hundred seventy-one".