21653213 has 4 divisors (see below), whose sum is σ = 21876540. Its totient is φ = 21429888.

The previous prime is 21653201. The next prime is 21653237. The reversal of 21653213 is 31235612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4826809 + 16826404 = 2197^2 + 4102^2 .

It is a cyclic number.

It is not a de Polignac number, because 21653213 - 2⁴ = 21653197 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21653243) 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, 111518 + ... + 111711.

It is an arithmetic number, because the mean of its divisors is an integer number (5469135).

Almost surely, 2^21653213 is an apocalyptic number.

It is an amenable number.

21653213 is a deficient number, since it is larger than the sum of its proper divisors (223327).

21653213 is an equidigital number, since it uses as much as digits as its factorization.

21653213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 223326.

The product of its digits is 1080, while the sum is 23.

The square root of 21653213 is about 4653.3013012269. The cubic root of 21653213 is about 278.7238395687.

Adding to 21653213 its reverse (31235612), we get a palindrome (52888825).

The spelling of 21653213 in words is "twenty-one million, six hundred fifty-three thousand, two hundred thirteen".