640642351 has 4 divisors (see below), whose sum is σ = 643464792. Its totient is φ = 637819912.

The previous prime is 640642349. The next prime is 640642367. The reversal of 640642351 is 153246046.

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 640642351 - 2¹ = 640642349 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640622351) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1410880 + ... + 1411333.

It is an arithmetic number, because the mean of its divisors is an integer number (160866198).

Almost surely, 2^640642351 is an apocalyptic number.

640642351 is a deficient number, since it is larger than the sum of its proper divisors (2822441).

640642351 is a wasteful number, since it uses less digits than its factorization.

640642351 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2822440.

The product of its (nonzero) digits is 17280, while the sum is 31.

The square root of 640642351 is about 25310.9136737495. The cubic root of 640642351 is about 862.0620927919.

Adding to 640642351 its reverse (153246046), we get a palindrome (793888397).

The spelling of 640642351 in words is "six hundred forty million, six hundred forty-two thousand, three hundred fifty-one".