21137213 has 4 divisors (see below), whose sum is σ = 21216060. Its totient is φ = 21058368.

The previous prime is 21137191. The next prime is 21137231. The reversal of 21137213 is 31273112.

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 9597604 + 11539609 = 3098^2 + 3397^2 .

It is a cyclic number.

It is not a de Polignac number, because 21137213 - 2¹⁴ = 21120829 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 (21137813) 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, 39020 + ... + 39557.

It is an arithmetic number, because the mean of its divisors is an integer number (5304015).

Almost surely, 2^21137213 is an apocalyptic number.

It is an amenable number.

21137213 is a deficient number, since it is larger than the sum of its proper divisors (78847).

21137213 is an equidigital number, since it uses as much as digits as its factorization.

21137213 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78846.

The product of its digits is 252, while the sum is 20.

The square root of 21137213 is about 4597.5224849912. The cubic root of 21137213 is about 276.4920029472.

The spelling of 21137213 in words is "twenty-one million, one hundred thirty-seven thousand, two hundred thirteen".