18661891 has 2 divisors, whose sum is σ = 18661892. Its totient is φ = 18661890.

The previous prime is 18661879. The next prime is 18661919. The reversal of 18661891 is 19816681.

It is a weak prime.

It is an emirp because it is prime and its reverse (19816681) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18661891 - 2⁵ = 18661859 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18661831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9330945 + 9330946.

It is an arithmetic number, because the mean of its divisors is an integer number (9330946).

Almost surely, 2^18661891 is an apocalyptic number.

18661891 is a deficient number, since it is larger than the sum of its proper divisors (1).

18661891 is an equidigital number, since it uses as much as digits as its factorization.

18661891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 40.

The square root of 18661891 is about 4319.9410875613. The cubic root of 18661891 is about 265.2478563935.

The spelling of 18661891 in words is "eighteen million, six hundred sixty-one thousand, eight hundred ninety-one".