20170921 has 8 divisors (see below), whose sum is σ = 21022920. Its totient is φ = 19329408.

The previous prime is 20170903. The next prime is 20170933. The reversal of 20170921 is 12907102.

It can be written as a sum of positive squares in 4 ways, for example, as 9517225 + 10653696 = 3085^2 + 3264^2 .

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 20170921 - 2¹¹ = 20168873 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20170892 and 20170901.

It is not an unprimeable number, because it can be changed into a prime (20170901) 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, 1435 + ... + 6511.

It is an arithmetic number, because the mean of its divisors is an integer number (2627865).

Almost surely, 2^20170921 is an apocalyptic number.

It is an amenable number.

20170921 is a deficient number, since it is larger than the sum of its proper divisors (851999).

20170921 is a wasteful number, since it uses less digits than its factorization.

20170921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5243.

The product of its (nonzero) digits is 252, while the sum is 22.

The square root of 20170921 is about 4491.2048494808. The cubic root of 20170921 is about 272.2128209319.

The spelling of 20170921 in words is "twenty million, one hundred seventy thousand, nine hundred twenty-one".