21072813 has 8 divisors (see below), whose sum is σ = 28120128. Its totient is φ = 14037024.

The previous prime is 21072769. The next prime is 21072823. The reversal of 21072813 is 31827012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21072813 - 2⁶ = 21072749 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21072823) 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, 3256 + ... + 7262.

It is an arithmetic number, because the mean of its divisors is an integer number (3515016).

Almost surely, 2^21072813 is an apocalyptic number.

It is an amenable number.

21072813 is a deficient number, since it is larger than the sum of its proper divisors (7047315).

21072813 is a wasteful number, since it uses less digits than its factorization.

21072813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5763.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 21072813 is about 4590.5133699838. The cubic root of 21072813 is about 276.2109157594.

Adding to 21072813 its reverse (31827012), we get a palindrome (52899825).

The spelling of 21072813 in words is "twenty-one million, seventy-two thousand, eight hundred thirteen".