21813791 has 4 divisors (see below), whose sum is σ = 21853512. Its totient is φ = 21774072.

The previous prime is 21813761. The next prime is 21813809. The reversal of 21813791 is 19731812.

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 21813791 - 2²² = 17619487 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21813731) 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, 19025 + ... + 20138.

It is an arithmetic number, because the mean of its divisors is an integer number (5463378).

Almost surely, 2^21813791 is an apocalyptic number.

21813791 is a deficient number, since it is larger than the sum of its proper divisors (39721).

21813791 is an equidigital number, since it uses as much as digits as its factorization.

21813791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39720.

The product of its digits is 3024, while the sum is 32.

The square root of 21813791 is about 4670.5236323136. The cubic root of 21813791 is about 279.4111391506.

The spelling of 21813791 in words is "twenty-one million, eight hundred thirteen thousand, seven hundred ninety-one".