640231531 has 4 divisors (see below), whose sum is σ = 640320912. Its totient is φ = 640142152.

The previous prime is 640231517. The next prime is 640231541. The reversal of 640231531 is 135132046.

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 640231531 - 2⁹ = 640231019 is a prime.

It is a super-2 number, since 2×640231531² = 819792826573207922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 640231496 and 640231505.

It is not an unprimeable number, because it can be changed into a prime (640231541) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32911 + ... + 48616.

It is an arithmetic number, because the mean of its divisors is an integer number (160080228).

Almost surely, 2^640231531 is an apocalyptic number.

640231531 is a deficient number, since it is larger than the sum of its proper divisors (89381).

640231531 is an equidigital number, since it uses as much as digits as its factorization.

640231531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 89380.

The product of its (nonzero) digits is 2160, while the sum is 25.

The square root of 640231531 is about 25302.7969007381. The cubic root of 640231531 is about 861.8777839874.

Adding to 640231531 its reverse (135132046), we get a palindrome (775363577).

The spelling of 640231531 in words is "six hundred forty million, two hundred thirty-one thousand, five hundred thirty-one".