21157807 has 4 divisors (see below), whose sum is σ = 23081256. Its totient is φ = 19234360.

The previous prime is 21157793. The next prime is 21157817. The reversal of 21157807 is 70875112.

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 21157807 - 2²³ = 12769199 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21157817) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 961708 + ... + 961729.

It is an arithmetic number, because the mean of its divisors is an integer number (5770314).

Almost surely, 2^21157807 is an apocalyptic number.

21157807 is a deficient number, since it is larger than the sum of its proper divisors (1923449).

21157807 is a wasteful number, since it uses less digits than its factorization.

21157807 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1923448.

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 21157807 is about 4599.7616242584. The cubic root of 21157807 is about 276.5817692448.

The spelling of 21157807 in words is "twenty-one million, one hundred fifty-seven thousand, eight hundred seven".