21579813 has 12 divisors (see below), whose sum is σ = 32176768. Its totient is φ = 13922280.

The previous prime is 21579809. The next prime is 21579821. The reversal of 21579813 is 31897512.

21579813 is a `hidden beast` number, since 2 + 1 + 579 + 81 + 3 = 666.

It is not a de Polignac number, because 21579813 - 2² = 21579809 is a prime.

It is a super-2 number, since 2×21579813² = 931376658229938, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21579853) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 38395 + ... + 38952.

Almost surely, 2^21579813 is an apocalyptic number.

It is an amenable number.

21579813 is a deficient number, since it is larger than the sum of its proper divisors (10596955).

21579813 is a wasteful number, since it uses less digits than its factorization.

21579813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 77384 (or 77381 counting only the distinct ones).

The product of its digits is 15120, while the sum is 36.

The square root of 21579813 is about 4645.4077323740. The cubic root of 21579813 is about 278.4085439436.

The spelling of 21579813 in words is "twenty-one million, five hundred seventy-nine thousand, eight hundred thirteen".