21328913 has 4 divisors (see below), whose sum is σ = 21690480. Its totient is φ = 20967348.

The previous prime is 21328907. The next prime is 21328919. The reversal of 21328913 is 31982312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (21328907) and next prime (21328919).

It is a cyclic number.

It is not a de Polignac number, because 21328913 - 2¹⁶ = 21263377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21328919) 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, 180695 + ... + 180812.

It is an arithmetic number, because the mean of its divisors is an integer number (5422620).

Almost surely, 2^21328913 is an apocalyptic number.

It is an amenable number.

21328913 is a deficient number, since it is larger than the sum of its proper divisors (361567).

21328913 is an equidigital number, since it uses as much as digits as its factorization.

21328913 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 361566.

The product of its digits is 2592, while the sum is 29.

The square root of 21328913 is about 4618.3236136070. The cubic root of 21328913 is about 277.3253528674.

The spelling of 21328913 in words is "twenty-one million, three hundred twenty-eight thousand, nine hundred thirteen".