20718809 has 2 divisors, whose sum is σ = 20718810. Its totient is φ = 20718808.

The previous prime is 20718781. The next prime is 20718823. The reversal of 20718809 is 90881702.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13579225 + 7139584 = 3685^2 + 2672^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20718809 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20718839) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10359404 + 10359405.

It is an arithmetic number, because the mean of its divisors is an integer number (10359405).

Almost surely, 2^20718809 is an apocalyptic number.

It is an amenable number.

20718809 is a deficient number, since it is larger than the sum of its proper divisors (1).

20718809 is an equidigital number, since it uses as much as digits as its factorization.

20718809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8064, while the sum is 35.

The square root of 20718809 is about 4551.7918449771. The cubic root of 20718809 is about 274.6554759936.

The spelling of 20718809 in words is "twenty million, seven hundred eighteen thousand, eight hundred nine".