18991309 has 2 divisors, whose sum is σ = 18991310. Its totient is φ = 18991308.

The previous prime is 18991303. The next prime is 18991319. The reversal of 18991309 is 90319981.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 9517225 + 9474084 = 3085^2 + 3078^2 .

It is an emirp because it is prime and its reverse (90319981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18991309 - 2¹⁹ = 18467021 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18991303) 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, 9495654 + 9495655.

It is an arithmetic number, because the mean of its divisors is an integer number (9495655).

Almost surely, 2^18991309 is an apocalyptic number.

It is an amenable number.

18991309 is a deficient number, since it is larger than the sum of its proper divisors (1).

18991309 is an equidigital number, since it uses as much as digits as its factorization.

18991309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 17496, while the sum is 40.

The square root of 18991309 is about 4357.9019034393. The cubic root of 18991309 is about 266.7994725640.

The spelling of 18991309 in words is "eighteen million, nine hundred ninety-one thousand, three hundred nine".