20917321 has 4 divisors (see below), whose sum is σ = 21482692. Its totient is φ = 20351952.

The previous prime is 20917313. The next prime is 20917331. The reversal of 20917321 is 12371902.

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 15210000 + 5707321 = 3900^2 + 2389^2 .

It is a cyclic number.

It is not a de Polignac number, because 20917321 - 2³ = 20917313 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20917331) 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, 282630 + ... + 282703.

It is an arithmetic number, because the mean of its divisors is an integer number (5370673).

Almost surely, 2^20917321 is an apocalyptic number.

It is an amenable number.

20917321 is a deficient number, since it is larger than the sum of its proper divisors (565371).

20917321 is an equidigital number, since it uses as much as digits as its factorization.

20917321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 565370.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 20917321 is about 4573.5457798080. The cubic root of 20917321 is about 275.5298698514.

The spelling of 20917321 in words is "twenty million, nine hundred seventeen thousand, three hundred twenty-one".