21017857 has 8 divisors (see below), whose sum is σ = 25284800. Its totient is φ = 17067024.

The previous prime is 21017809. The next prime is 21017861. The reversal of 21017857 is 75871012.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21017857 - 2¹¹ = 21015809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21017897) 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, 78882 + ... + 79147.

It is an arithmetic number, because the mean of its divisors is an integer number (3160600).

Almost surely, 2^21017857 is an apocalyptic number.

It is an amenable number.

21017857 is a deficient number, since it is larger than the sum of its proper divisors (4266943).

21017857 is a wasteful number, since it uses less digits than its factorization.

21017857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 158055.

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 21017857 is about 4584.5236393763. The cubic root of 21017857 is about 275.9705956562.

Adding to 21017857 its reverse (75871012), we get a palindrome (96888869).

The spelling of 21017857 in words is "twenty-one million, seventeen thousand, eight hundred fifty-seven".