21680857 has 4 divisors (see below), whose sum is σ = 23651856. Its totient is φ = 19709860.

The previous prime is 21680849. The next prime is 21680861. The reversal of 21680857 is 75808612.

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 21680857 - 2³ = 21680849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21680807) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 985483 + ... + 985504.

It is an arithmetic number, because the mean of its divisors is an integer number (5912964).

Almost surely, 2^21680857 is an apocalyptic number.

It is an amenable number.

21680857 is a deficient number, since it is larger than the sum of its proper divisors (1970999).

21680857 is a wasteful number, since it uses less digits than its factorization.

21680857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1970998.

The product of its (nonzero) digits is 26880, while the sum is 37.

The square root of 21680857 is about 4656.2707180747. The cubic root of 21680857 is about 278.8424018842.

The spelling of 21680857 in words is "twenty-one million, six hundred eighty thousand, eight hundred fifty-seven".