21785857 has 4 divisors (see below), whose sum is σ = 23067396. Its totient is φ = 20504320.

The previous prime is 21785851. The next prime is 21785867. The reversal of 21785857 is 75858712.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6739216 + 15046641 = 2596^2 + 3879^2 .

It is a cyclic number.

It is not a de Polignac number, because 21785857 - 2³ = 21785849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21785851) 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, 640744 + ... + 640777.

It is an arithmetic number, because the mean of its divisors is an integer number (5766849).

Almost surely, 2^21785857 is an apocalyptic number.

It is an amenable number.

21785857 is a deficient number, since it is larger than the sum of its proper divisors (1281539).

21785857 is a wasteful number, since it uses less digits than its factorization.

21785857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1281538.

The product of its digits is 156800, while the sum is 43.

The square root of 21785857 is about 4667.5322173500. The cubic root of 21785857 is about 279.2918200653.

The spelling of 21785857 in words is "twenty-one million, seven hundred eighty-five thousand, eight hundred fifty-seven".