20805921 has 6 divisors (see below), whose sum is σ = 30053010. Its totient is φ = 13870608.

The previous prime is 20805907. The next prime is 20805923. The reversal of 20805921 is 12950802.

It can be written as a sum of positive squares in only one way, i.e., 20793600 + 12321 = 4560^2 + 111^2 .

It is not a de Polignac number, because 20805921 - 2¹⁰ = 20804897 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20805923) 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 5 ways as a sum of consecutive naturals, for example, 1155876 + ... + 1155893.

It is an arithmetic number, because the mean of its divisors is an integer number (5008835).

Almost surely, 2^20805921 is an apocalyptic number.

It is an amenable number.

20805921 is a deficient number, since it is larger than the sum of its proper divisors (9247089).

20805921 is a wasteful number, since it uses less digits than its factorization.

20805921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2311775 (or 2311772 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 20805921 is about 4561.3507867736. The cubic root of 20805921 is about 275.0398663966.

It can be divided in two parts, 2080 and 5921, that added together give a triangular number (8001 = T₁₂₆).

The spelling of 20805921 in words is "twenty million, eight hundred five thousand, nine hundred twenty-one".