18938921 has 2 divisors, whose sum is σ = 18938922. Its totient is φ = 18938920.

The previous prime is 18938911. The next prime is 18938947. The reversal of 18938921 is 12983981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17472400 + 1466521 = 4180^2 + 1211^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18938921 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (18938911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9469460 + 9469461.

It is an arithmetic number, because the mean of its divisors is an integer number (9469461).

Almost surely, 2^18938921 is an apocalyptic number.

It is an amenable number.

18938921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18938921 is an equidigital number, since it uses as much as digits as its factorization.

18938921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 41.

The square root of 18938921 is about 4351.8870619537. The cubic root of 18938921 is about 266.5539223047.

The spelling of 18938921 in words is "eighteen million, nine hundred thirty-eight thousand, nine hundred twenty-one".