21213851 has 4 divisors (see below), whose sum is σ = 21731304. Its totient is φ = 20696400.

The previous prime is 21213847. The next prime is 21213853. The reversal of 21213851 is 15831212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21213851 - 2² = 21213847 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21213853) 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, 258665 + ... + 258746.

It is an arithmetic number, because the mean of its divisors is an integer number (5432826).

Almost surely, 2^21213851 is an apocalyptic number.

21213851 is a deficient number, since it is larger than the sum of its proper divisors (517453).

21213851 is an equidigital number, since it uses as much as digits as its factorization.

21213851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 517452.

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

The square root of 21213851 is about 4605.8496501731. The cubic root of 21213851 is about 276.8257624331.

The spelling of 21213851 in words is "twenty-one million, two hundred thirteen thousand, eight hundred fifty-one".