18721891 has 2 divisors, whose sum is σ = 18721892. Its totient is φ = 18721890.

The previous prime is 18721883. The next prime is 18721903. The reversal of 18721891 is 19812781.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 18721891 - 2³ = 18721883 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 18721891.

It is not a weakly prime, because it can be changed into another prime (18721841) 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 as a sum of consecutive naturals, namely, 9360945 + 9360946.

It is an arithmetic number, because the mean of its divisors is an integer number (9360946).

Almost surely, 2^18721891 is an apocalyptic number.

18721891 is a deficient number, since it is larger than the sum of its proper divisors (1).

18721891 is an equidigital number, since it uses as much as digits as its factorization.

18721891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 37.

The square root of 18721891 is about 4326.8800538032. The cubic root of 18721891 is about 265.5318191454.

The spelling of 18721891 in words is "eighteen million, seven hundred twenty-one thousand, eight hundred ninety-one".