640561 has 4 divisors (see below), whose sum is σ = 651124. Its totient is φ = 630000.

The previous prime is 640531. The next prime is 640579. The reversal of 640561 is 165046.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 87025 + 553536 = 295^2 + 744^2 .

It is a cyclic number.

It is not a de Polignac number, because 640561 - 2⁵ = 640529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640531) 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, 5190 + ... + 5311.

It is an arithmetic number, because the mean of its divisors is an integer number (162781).

2⁶⁴⁰⁵⁶¹ is an apocalyptic number.

640561 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

640561 is a deficient number, since it is larger than the sum of its proper divisors (10563).

640561 is a wasteful number, since it uses less digits than its factorization.

640561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10562.

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 640561 is about 800.3505481975. The cubic root of 640561 is about 86.2025602030.

The spelling of 640561 in words is "six hundred forty thousand, five hundred sixty-one".