21745213 has 4 divisors (see below), whose sum is σ = 24851680. Its totient is φ = 18638748.

The previous prime is 21745201. The next prime is 21745247. The reversal of 21745213 is 31254712.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 21745213 - 2⁵ = 21745181 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21745613) 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, 1553223 + ... + 1553236.

It is an arithmetic number, because the mean of its divisors is an integer number (6212920).

Almost surely, 2^21745213 is an apocalyptic number.

It is an amenable number.

21745213 is a deficient number, since it is larger than the sum of its proper divisors (3106467).

21745213 is an equidigital number, since it uses as much as digits as its factorization.

21745213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3106466.

The product of its digits is 1680, while the sum is 25.

The square root of 21745213 is about 4663.1762780320. The cubic root of 21745213 is about 279.1180283671.

Adding to 21745213 its reverse (31254712), we get a palindrome (52999925).

The spelling of 21745213 in words is "twenty-one million, seven hundred forty-five thousand, two hundred thirteen".