20128561 has 10 divisors (see below), whose sum is σ = 21475322. Its totient is φ = 18865920.

The previous prime is 20128553. The next prime is 20128573. The reversal of 20128561 is 16582102.

20128561 is nontrivially palindromic in base 4 and base 16.

It can be written as a sum of positive squares in 5 ways, for example, as 2117025 + 18011536 = 1455^2 + 4244^2 .

It is not a de Polignac number, because 20128561 - 2³ = 20128553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20128501) 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 9 ways as a sum of consecutive naturals, for example, 83401 + ... + 83641.

Almost surely, 2^20128561 is an apocalyptic number.

It is an amenable number.

20128561 is a deficient number, since it is larger than the sum of its proper divisors (1346761).

20128561 is an frugal number, since it uses more digits than its factorization.

20128561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 309 (or 258 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 20128561 is about 4486.4864872191. The cubic root of 20128561 is about 272.0221336155.

The spelling of 20128561 in words is "twenty million, one hundred twenty-eight thousand, five hundred sixty-one".