20945821 has 4 divisors (see below), whose sum is σ = 22557052. Its totient is φ = 19334592.

The previous prime is 20945807. The next prime is 20945833. The reversal of 20945821 is 12854902.

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 9796900 + 11148921 = 3130^2 + 3339^2 .

It is a cyclic number.

It is not a de Polignac number, because 20945821 - 2⁵ = 20945789 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 (20945851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 805596 + ... + 805621.

It is an arithmetic number, because the mean of its divisors is an integer number (5639263).

Almost surely, 2^20945821 is an apocalyptic number.

It is an amenable number.

20945821 is a deficient number, since it is larger than the sum of its proper divisors (1611231).

20945821 is a wasteful number, since it uses less digits than its factorization.

20945821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1611230.

The product of its (nonzero) digits is 5760, while the sum is 31.

The square root of 20945821 is about 4576.6604637006. The cubic root of 20945821 is about 275.6549502027.

The spelling of 20945821 in words is "twenty million, nine hundred forty-five thousand, eight hundred twenty-one".