20821109 has 4 divisors (see below), whose sum is σ = 20834604. Its totient is φ = 20807616.

The previous prime is 20821081. The next prime is 20821117. The reversal of 20821109 is 90112802.

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 3598609 + 17222500 = 1897^2 + 4150^2 .

It is a cyclic number.

It is not a de Polignac number, because 20821109 - 2¹⁶ = 20755573 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20821309) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4082 + ... + 7635.

It is an arithmetic number, because the mean of its divisors is an integer number (5208651).

Almost surely, 2^20821109 is an apocalyptic number.

It is an amenable number.

20821109 is a deficient number, since it is larger than the sum of its proper divisors (13495).

20821109 is a wasteful number, since it uses less digits than its factorization.

20821109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13494.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 20821109 is about 4563.0153407588. The cubic root of 20821109 is about 275.1067750657.

The spelling of 20821109 in words is "twenty million, eight hundred twenty-one thousand, one hundred nine".