18991121 has 2 divisors, whose sum is σ = 18991122. Its totient is φ = 18991120.

The previous prime is 18991117. The next prime is 18991129. The reversal of 18991121 is 12119981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13608721 + 5382400 = 3689^2 + 2320^2 .

It is a cyclic number.

It is not a de Polignac number, because 18991121 - 2² = 18991117 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (18991129) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9495560 + 9495561.

It is an arithmetic number, because the mean of its divisors is an integer number (9495561).

Almost surely, 2^18991121 is an apocalyptic number.

It is an amenable number.

18991121 is a deficient number, since it is larger than the sum of its proper divisors (1).

18991121 is an equidigital number, since it uses as much as digits as its factorization.

18991121 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1296, while the sum is 32.

The square root of 18991121 is about 4357.8803333731. The cubic root of 18991121 is about 266.7985921882.

The spelling of 18991121 in words is "eighteen million, nine hundred ninety-one thousand, one hundred twenty-one".