20718409 has 8 divisors (see below), whose sum is σ = 21358280. Its totient is φ = 20082816.

The previous prime is 20718403. The next prime is 20718413. The reversal of 20718409 is 90481702.

It can be written as a sum of positive squares in 4 ways, for example, as 5508409 + 15210000 = 2347^2 + 3900^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 20718409 - 2⁷ = 20718281 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20718403) 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 in 7 ways as a sum of consecutive naturals, for example, 10687 + ... + 12475.

It is an arithmetic number, because the mean of its divisors is an integer number (2669785).

Almost surely, 2^20718409 is an apocalyptic number.

It is an amenable number.

20718409 is a deficient number, since it is larger than the sum of its proper divisors (639871).

20718409 is a wasteful number, since it uses less digits than its factorization.

20718409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2139.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 20718409 is about 4551.7479060247. The cubic root of 20718409 is about 274.6537084708.

The spelling of 20718409 in words is "twenty million, seven hundred eighteen thousand, four hundred nine".