20915891 has 2 divisors, whose sum is σ = 20915892. Its totient is φ = 20915890.

The previous prime is 20915857. The next prime is 20915911. The reversal of 20915891 is 19851902.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20915891 - 2¹⁰ = 20914867 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20912891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10457945 + 10457946.

It is an arithmetic number, because the mean of its divisors is an integer number (10457946).

Almost surely, 2^20915891 is an apocalyptic number.

20915891 is a deficient number, since it is larger than the sum of its proper divisors (1).

20915891 is an equidigital number, since it uses as much as digits as its factorization.

20915891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6480, while the sum is 35.

The square root of 20915891 is about 4573.3894432904. The cubic root of 20915891 is about 275.5235908973.

The spelling of 20915891 in words is "twenty million, nine hundred fifteen thousand, eight hundred ninety-one".