18909509 has 2 divisors, whose sum is σ = 18909510. Its totient is φ = 18909508.

The previous prime is 18909497. The next prime is 18909511. The reversal of 18909509 is 90590981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15288100 + 3621409 = 3910^2 + 1903^2 .

It is a cyclic number.

It is not a de Polignac number, because 18909509 - 2⁴ = 18909493 is a prime.

Together with 18909511, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18909529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9454754 + 9454755.

It is an arithmetic number, because the mean of its divisors is an integer number (9454755).

Almost surely, 2^18909509 is an apocalyptic number.

It is an amenable number.

18909509 is a deficient number, since it is larger than the sum of its proper divisors (1).

18909509 is an equidigital number, since it uses as much as digits as its factorization.

18909509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 29160, while the sum is 41.

The square root of 18909509 is about 4348.5065252337. The cubic root of 18909509 is about 266.4158654095.

The spelling of 18909509 in words is "eighteen million, nine hundred nine thousand, five hundred nine".