20715509 has 4 divisors (see below), whose sum is σ = 20726700. Its totient is φ = 20704320.

The previous prime is 20715493. The next prime is 20715517. The reversal of 20715509 is 90551702.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 90551702 = 2 ⋅45275851.

It can be written as a sum of positive squares in 2 ways, for example, as 4635409 + 16080100 = 2153^2 + 4010^2 .

It is a cyclic number.

It is not a de Polignac number, because 20715509 - 2⁴ = 20715493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20715589) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2084 + ... + 6765.

It is an arithmetic number, because the mean of its divisors is an integer number (5181675).

Almost surely, 2^20715509 is an apocalyptic number.

It is an amenable number.

20715509 is a deficient number, since it is larger than the sum of its proper divisors (11191).

20715509 is an equidigital number, since it uses as much as digits as its factorization.

20715509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11190.

The product of its (nonzero) digits is 3150, while the sum is 29.

The square root of 20715509 is about 4551.4293359339. The cubic root of 20715509 is about 274.6408932507.

The spelling of 20715509 in words is "twenty million, seven hundred fifteen thousand, five hundred nine".