21313921 has 4 divisors (see below), whose sum is σ = 21325572. Its totient is φ = 21302272.

The previous prime is 21313913. The next prime is 21313931. The reversal of 21313921 is 12931312.

21313921 = 3264² + 3265².

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 can be written as a sum of positive squares in 2 ways, for example, as 10660225 + 10653696 = 3265^2 + 3264^2 .

It is a cyclic number.

It is not a de Polignac number, because 21313921 - 2³ = 21313913 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21313892 and 21313901.

It is not an unprimeable number, because it can be changed into a prime (21313931) 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, 2416 + ... + 6961.

It is an arithmetic number, because the mean of its divisors is an integer number (5331393).

Almost surely, 2^21313921 is an apocalyptic number.

21313921 is the 3265-th centered square number.

It is an amenable number.

21313921 is a deficient number, since it is larger than the sum of its proper divisors (11651).

21313921 is an equidigital number, since it uses as much as digits as its factorization.

21313921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11650.

The product of its digits is 324, while the sum is 22.

The square root of 21313921 is about 4616.7002285182. The cubic root of 21313921 is about 277.2603607101.

The spelling of 21313921 in words is "twenty-one million, three hundred thirteen thousand, nine hundred twenty-one".