21851213 has 4 divisors (see below), whose sum is σ = 21861180. Its totient is φ = 21841248.

The previous prime is 21851189. The next prime is 21851227. The reversal of 21851213 is 31215812.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 16752649 + 5098564 = 4093^2 + 2258^2 .

It is a cyclic number.

It is not a de Polignac number, because 21851213 - 2⁸ = 21850957 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 (21851233) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 98 + ... + 6611.

It is an arithmetic number, because the mean of its divisors is an integer number (5465295).

Almost surely, 2^21851213 is an apocalyptic number.

It is an amenable number.

21851213 is a deficient number, since it is larger than the sum of its proper divisors (9967).

21851213 is an equidigital number, since it uses as much as digits as its factorization.

21851213 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9966.

The product of its digits is 480, while the sum is 23.

The square root of 21851213 is about 4674.5281045256. The cubic root of 21851213 is about 279.5708263582.

The spelling of 21851213 in words is "twenty-one million, eight hundred fifty-one thousand, two hundred thirteen".