640191555921 has 16 divisors (see below), whose sum is σ = 854376766848. Its totient is φ = 426400540800.

The previous prime is 640191555901. The next prime is 640191555931. The reversal of 640191555921 is 129555191046.

It is not a de Polignac number, because 640191555921 - 2²² = 640187361617 is a prime.

It is not an unprimeable number, because it can be changed into a prime (640191555901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 15563101 + ... + 15604181.

It is an arithmetic number, because the mean of its divisors is an integer number (53398547928).

Almost surely, 2^640191555921 is an apocalyptic number.

It is an amenable number.

640191555921 is a deficient number, since it is larger than the sum of its proper divisors (214185210927).

640191555921 is a wasteful number, since it uses less digits than its factorization.

640191555921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45752.

The product of its (nonzero) digits is 486000, while the sum is 48.

The spelling of 640191555921 in words is "six hundred forty billion, one hundred ninety-one million, five hundred fifty-five thousand, nine hundred twenty-one".