21508213 has 8 divisors (see below), whose sum is σ = 23303808. Its totient is φ = 19771584.

The previous prime is 21508181. The next prime is 21508217. The reversal of 21508213 is 31280512.

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 21508213 - 2⁵ = 21508181 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 (21508217) 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, 13981 + ... + 15442.

It is an arithmetic number, because the mean of its divisors is an integer number (2912976).

Almost surely, 2^21508213 is an apocalyptic number.

It is an amenable number.

21508213 is a deficient number, since it is larger than the sum of its proper divisors (1795595).

21508213 is a wasteful number, since it uses less digits than its factorization.

21508213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29483.

The product of its (nonzero) digits is 480, while the sum is 22.

The square root of 21508213 is about 4637.6947937526. The cubic root of 21508213 is about 278.1002907476.

Adding to 21508213 its reverse (31280512), we get a palindrome (52788725).

The spelling of 21508213 in words is "twenty-one million, five hundred eight thousand, two hundred thirteen".