18013921 has 2 divisors, whose sum is σ = 18013922. Its totient is φ = 18013920.

The previous prime is 18013913. The next prime is 18013981. The reversal of 18013921 is 12931081.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17943696 + 70225 = 4236^2 + 265^2 .

It is an emirp because it is prime and its reverse (12931081) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18013921 - 2³ = 18013913 is a prime.

It is not a weakly prime, because it can be changed into another prime (18013981) 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, 9006960 + 9006961.

It is an arithmetic number, because the mean of its divisors is an integer number (9006961).

Almost surely, 2^18013921 is an apocalyptic number.

It is an amenable number.

18013921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18013921 is an equidigital number, since it uses as much as digits as its factorization.

18013921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 18013921 is about 4244.2809756188. The cubic root of 18013921 is about 262.1416837537.

The spelling of 18013921 in words is "eighteen million, thirteen thousand, nine hundred twenty-one".