21521857 has 8 divisors (see below), whose sum is σ = 25444800. Its totient is φ = 17811024.

The previous prime is 21521849. The next prime is 21521893. The reversal of 21521857 is 75812512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21521857 - 2³ = 21521849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21521257) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 52807 + ... + 53212.

It is an arithmetic number, because the mean of its divisors is an integer number (3180600).

Almost surely, 2^21521857 is an apocalyptic number.

It is an amenable number.

21521857 is a deficient number, since it is larger than the sum of its proper divisors (3922943).

21521857 is a wasteful number, since it uses less digits than its factorization.

21521857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 106055.

The product of its digits is 5600, while the sum is 31.

The square root of 21521857 is about 4639.1655499669. The cubic root of 21521857 is about 278.1590837664.

The spelling of 21521857 in words is "twenty-one million, five hundred twenty-one thousand, eight hundred fifty-seven".