20910805921 has 2 divisors, whose sum is σ = 20910805922. Its totient is φ = 20910805920.

The previous prime is 20910805913. The next prime is 20910806011. The reversal of 20910805921 is 12950801902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20812101696 + 98704225 = 144264^2 + 9935^2 .

It is a cyclic number.

It is not a de Polignac number, because 20910805921 - 2³ = 20910805913 is a prime.

It is not a weakly prime, because it can be changed into another prime (20910805021) 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 as a sum of consecutive naturals, namely, 10455402960 + 10455402961.

It is an arithmetic number, because the mean of its divisors is an integer number (10455402961).

Almost surely, 2^20910805921 is an apocalyptic number.

It is an amenable number.

20910805921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20910805921 is an equidigital number, since it uses as much as digits as its factorization.

20910805921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 12960, while the sum is 37.

The spelling of 20910805921 in words is "twenty billion, nine hundred ten million, eight hundred five thousand, nine hundred twenty-one".