20815891 has 2 divisors, whose sum is σ = 20815892. Its totient is φ = 20815890.

The previous prime is 20815889. The next prime is 20815919. The reversal of 20815891 is 19851802.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 20815891 - 2¹ = 20815889 is a prime.

Together with 20815889, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20815801) 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, 10407945 + 10407946.

It is an arithmetic number, because the mean of its divisors is an integer number (10407946).

Almost surely, 2^20815891 is an apocalyptic number.

20815891 is a deficient number, since it is larger than the sum of its proper divisors (1).

20815891 is an equidigital number, since it uses as much as digits as its factorization.

20815891 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 20815891 is about 4562.4435338972. The cubic root of 20815891 is about 275.0837915463.

The spelling of 20815891 in words is "twenty million, eight hundred fifteen thousand, eight hundred ninety-one".