640531 has 2 divisors, whose sum is σ = 640532. Its totient is φ = 640530.

The previous prime is 640529. The next prime is 640579. The reversal of 640531 is 135046.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 640531 - 2¹ = 640529 is a prime.

It is a super-2 number, since 2×640531² = 820559923922, which contains 22 as substring.

Together with 640529, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 640499 and 640508.

It is not a weakly prime, because it can be changed into another prime (640231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320265 + 320266.

It is an arithmetic number, because the mean of its divisors is an integer number (320266).

2⁶⁴⁰⁵³¹ is an apocalyptic number.

640531 is a deficient number, since it is larger than the sum of its proper divisors (1).

640531 is an equidigital number, since it uses as much as digits as its factorization.

640531 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 360, while the sum is 19.

The square root of 640531 is about 800.3318061904. The cubic root of 640531 is about 86.2012144466.

Adding to 640531 its reverse (135046), we get a palindrome (775577).

The spelling of 640531 in words is "six hundred forty thousand, five hundred thirty-one".