21179857 has 4 divisors (see below), whose sum is σ = 21435120. Its totient is φ = 20924596.

The previous prime is 21179843. The next prime is 21179861. The reversal of 21179857 is 75897112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21179857 - 2⁷ = 21179729 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21179827) 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, 127507 + ... + 127672.

It is an arithmetic number, because the mean of its divisors is an integer number (5358780).

Almost surely, 2^21179857 is an apocalyptic number.

It is an amenable number.

21179857 is a deficient number, since it is larger than the sum of its proper divisors (255263).

21179857 is an equidigital number, since it uses as much as digits as its factorization.

21179857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 255262.

The product of its digits is 35280, while the sum is 40.

The square root of 21179857 is about 4602.1578634375. The cubic root of 21179857 is about 276.6778174890.

The spelling of 21179857 in words is "twenty-one million, one hundred seventy-nine thousand, eight hundred fifty-seven".