21640799 has 4 divisors (see below), whose sum is σ = 21963864. Its totient is φ = 21317736.

The previous prime is 21640789. The next prime is 21640811. The reversal of 21640799 is 99704612.

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 21640799 - 2⁴ = 21640783 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 (21640789) 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, 161432 + ... + 161565.

It is an arithmetic number, because the mean of its divisors is an integer number (5490966).

Almost surely, 2^21640799 is an apocalyptic number.

21640799 is a deficient number, since it is larger than the sum of its proper divisors (323065).

21640799 is an equidigital number, since it uses as much as digits as its factorization.

21640799 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 323064.

The product of its (nonzero) digits is 27216, while the sum is 38.

The square root of 21640799 is about 4651.9672182852. The cubic root of 21640799 is about 278.6705643467.

The spelling of 21640799 in words is "twenty-one million, six hundred forty thousand, seven hundred ninety-nine".