640251391 has 16 divisors (see below), whose sum is σ = 729360576. Its totient is φ = 557542656.

The previous prime is 640251389. The next prime is 640251407. The reversal of 640251391 is 193152046.

It is a cyclic number.

It is not a de Polignac number, because 640251391 - 2¹ = 640251389 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640251301) 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, 7161 + ... + 36493.

It is an arithmetic number, because the mean of its divisors is an integer number (45585036).

Almost surely, 2^640251391 is an apocalyptic number.

640251391 is a deficient number, since it is larger than the sum of its proper divisors (89109185).

640251391 is a wasteful number, since it uses less digits than its factorization.

640251391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29442.

The product of its (nonzero) digits is 6480, while the sum is 31.

The square root of 640251391 is about 25303.1893444285. The cubic root of 640251391 is about 861.8866957196.

The spelling of 640251391 in words is "six hundred forty million, two hundred fifty-one thousand, three hundred ninety-one".