21120813 has 36 divisors (see below), whose sum is σ = 36279360. Its totient is φ = 11800656.

The previous prime is 21120811. The next prime is 21120829. The reversal of 21120813 is 31802112.

It is not a de Polignac number, because 21120813 - 2¹ = 21120811 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21120811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 20218 + ... + 21236.

It is an arithmetic number, because the mean of its divisors is an integer number (1007760).

Almost surely, 2^21120813 is an apocalyptic number.

It is an amenable number.

21120813 is a deficient number, since it is larger than the sum of its proper divisors (15158547).

21120813 is a wasteful number, since it uses less digits than its factorization.

21120813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1086 (or 1076 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21120813 is about 4595.7385695881. The cubic root of 21120813 is about 276.4204759820.

Adding to 21120813 its reverse (31802112), we get a palindrome (52922925).

The spelling of 21120813 in words is "twenty-one million, one hundred twenty thousand, eight hundred thirteen".