18847991 has 2 divisors, whose sum is σ = 18847992. Its totient is φ = 18847990.

The previous prime is 18847937. The next prime is 18847993. The reversal of 18847991 is 19974881.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 18847991 - 2¹⁰ = 18846967 is a prime.

Together with 18847993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18847993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9423995 + 9423996.

It is an arithmetic number, because the mean of its divisors is an integer number (9423996).

Almost surely, 2^18847991 is an apocalyptic number.

18847991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18847991 is an equidigital number, since it uses as much as digits as its factorization.

18847991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 145152, while the sum is 47.

The square root of 18847991 is about 4341.4272998635. The cubic root of 18847991 is about 266.1266427315.

The spelling of 18847991 in words is "eighteen million, eight hundred forty-seven thousand, nine hundred ninety-one".