20816591 has 4 divisors (see below), whose sum is σ = 20826000. Its totient is φ = 20807184.

The previous prime is 20816569. The next prime is 20816597. The reversal of 20816591 is 19561802.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20816591 - 2⁶ = 20816527 is a prime.

It is a super-2 number, since 2×20816591² = 866660921722562, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20816597) 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, 635 + ... + 6483.

It is an arithmetic number, because the mean of its divisors is an integer number (5206500).

Almost surely, 2^20816591 is an apocalyptic number.

20816591 is a deficient number, since it is larger than the sum of its proper divisors (9409).

20816591 is an equidigital number, since it uses as much as digits as its factorization.

20816591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9408.

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 20816591 is about 4562.5202465304. The cubic root of 20816591 is about 275.0868750318.

The spelling of 20816591 in words is "twenty million, eight hundred sixteen thousand, five hundred ninety-one".