21320891 has 8 divisors (see below), whose sum is σ = 21843024. Its totient is φ = 20805120.

The previous prime is 21320881. The next prime is 21320911. The reversal of 21320891 is 19802312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21320891 - 2¹⁸ = 21058747 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 21320891.

It is not an unprimeable number, because it can be changed into a prime (21320801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5576 + ... + 8586.

It is an arithmetic number, because the mean of its divisors is an integer number (2730378).

Almost surely, 2^21320891 is an apocalyptic number.

21320891 is a deficient number, since it is larger than the sum of its proper divisors (522133).

21320891 is an equidigital number, since it uses as much as digits as its factorization.

21320891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3181.

The product of its (nonzero) digits is 864, while the sum is 26.

The square root of 21320891 is about 4617.4550349733. The cubic root of 21320891 is about 277.2905803038.

The spelling of 21320891 in words is "twenty-one million, three hundred twenty thousand, eight hundred ninety-one".