20561807 has 4 divisors (see below), whose sum is σ = 23499216. Its totient is φ = 17624400.

The previous prime is 20561797. The next prime is 20561809. The reversal of 20561807 is 70816502.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 70816502 = 2 ⋅35408251.

It is a cyclic number.

It is not a de Polignac number, because 20561807 - 2¹² = 20557711 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20561807.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20561809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1468694 + ... + 1468707.

It is an arithmetic number, because the mean of its divisors is an integer number (5874804).

Almost surely, 2^20561807 is an apocalyptic number.

20561807 is a deficient number, since it is larger than the sum of its proper divisors (2937409).

20561807 is an equidigital number, since it uses as much as digits as its factorization.

20561807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2937408.

The product of its (nonzero) digits is 3360, while the sum is 29.

The square root of 20561807 is about 4534.5128735069. The cubic root of 20561807 is about 273.9599591622.

The spelling of 20561807 in words is "twenty million, five hundred sixty-one thousand, eight hundred seven".