20128509 has 12 divisors (see below), whose sum is σ = 29473756. Its totient is φ = 13234752.

The previous prime is 20128501. The next prime is 20128513. The reversal of 20128509 is 90582102.

It can be written as a sum of positive squares in 2 ways, for example, as 16040025 + 4088484 = 4005^2 + 2022^2 .

It is not a de Polignac number, because 20128509 - 2³ = 20128501 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 (20128501) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14662 + ... + 15975.

Almost surely, 2^20128509 is an apocalyptic number.

It is an amenable number.

20128509 is a deficient number, since it is larger than the sum of its proper divisors (9345247).

20128509 is a wasteful number, since it uses less digits than its factorization.

20128509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30716 (or 30713 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 20128509 is about 4486.4806920347. The cubic root of 20128509 is about 272.0218993686.

The spelling of 20128509 in words is "twenty million, one hundred twenty-eight thousand, five hundred nine".