18643991 has 2 divisors, whose sum is σ = 18643992. Its totient is φ = 18643990.

The previous prime is 18643949. The next prime is 18644011. The reversal of 18643991 is 19934681.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18643991 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18643901) 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, 9321995 + 9321996.

It is an arithmetic number, because the mean of its divisors is an integer number (9321996).

Almost surely, 2^18643991 is an apocalyptic number.

18643991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18643991 is an equidigital number, since it uses as much as digits as its factorization.

18643991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 46656, while the sum is 41.

The square root of 18643991 is about 4317.8688030092. The cubic root of 18643991 is about 265.1630229850.

The spelling of 18643991 in words is "eighteen million, six hundred forty-three thousand, nine hundred ninety-one".