21644213 has 8 divisors (see below), whose sum is σ = 23094720. Its totient is φ = 20213440.

The previous prime is 21644197. The next prime is 21644257. The reversal of 21644213 is 31244612.

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 21644213 - 2⁴ = 21644197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21644113) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2633 + ... + 7086.

It is an arithmetic number, because the mean of its divisors is an integer number (2886840).

Almost surely, 2^21644213 is an apocalyptic number.

It is an amenable number.

21644213 is a deficient number, since it is larger than the sum of its proper divisors (1450507).

21644213 is a wasteful number, since it uses less digits than its factorization.

21644213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9867.

The product of its digits is 1152, while the sum is 23.

The square root of 21644213 is about 4652.3341453511. The cubic root of 21644213 is about 278.6852177071.

Adding to 21644213 its reverse (31244612), we get a palindrome (52888825).

The spelling of 21644213 in words is "twenty-one million, six hundred forty-four thousand, two hundred thirteen".