640236731 has 4 divisors (see below), whose sum is σ = 640616592. Its totient is φ = 639856872.

The previous prime is 640236721. The next prime is 640236743. The reversal of 640236731 is 137632046.

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 640236731 - 2²² = 636042427 is a prime.

It is a super-2 number, since 2×640236731² = 819806143443132722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640236721) 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, 187391 + ... + 190776.

It is an arithmetic number, because the mean of its divisors is an integer number (160154148).

Almost surely, 2^640236731 is an apocalyptic number.

640236731 is a deficient number, since it is larger than the sum of its proper divisors (379861).

640236731 is a wasteful number, since it uses less digits than its factorization.

640236731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 379860.

The product of its (nonzero) digits is 18144, while the sum is 32.

The square root of 640236731 is about 25302.8996559683. The cubic root of 640236731 is about 861.8801173893.

Adding to 640236731 its reverse (137632046), we get a palindrome (777868777).

The spelling of 640236731 in words is "six hundred forty million, two hundred thirty-six thousand, seven hundred thirty-one".