21657859 has 4 divisors (see below), whose sum is σ = 21954616. Its totient is φ = 21361104.

The previous prime is 21657833. The next prime is 21657863. The reversal of 21657859 is 95875612.

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 21657859 - 2⁷ = 21657731 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21657829) 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 3 ways as a sum of consecutive naturals, for example, 148269 + ... + 148414.

It is an arithmetic number, because the mean of its divisors is an integer number (5488654).

Almost surely, 2^21657859 is an apocalyptic number.

21657859 is a deficient number, since it is larger than the sum of its proper divisors (296757).

21657859 is an equidigital number, since it uses as much as digits as its factorization.

21657859 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 296756.

The product of its digits is 151200, while the sum is 43.

The square root of 21657859 is about 4653.8004899222. The cubic root of 21657859 is about 278.7437728438.

The spelling of 21657859 in words is "twenty-one million, six hundred fifty-seven thousand, eight hundred fifty-nine".