20990891 has 2 divisors, whose sum is σ = 20990892. Its totient is φ = 20990890.

The previous prime is 20990863. The next prime is 20990911. The reversal of 20990891 is 19809902.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20990891 - 2¹⁰ = 20989867 is a prime.

It is not a weakly prime, because it can be changed into another prime (20990821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10495445 + 10495446.

It is an arithmetic number, because the mean of its divisors is an integer number (10495446).

Almost surely, 2^20990891 is an apocalyptic number.

20990891 is a deficient number, since it is larger than the sum of its proper divisors (1).

20990891 is an equidigital number, since it uses as much as digits as its factorization.

20990891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 11664, while the sum is 38.

The square root of 20990891 is about 4581.5817137753. The cubic root of 20990891 is about 275.8525213289.

The spelling of 20990891 in words is "twenty million, nine hundred ninety thousand, eight hundred ninety-one".