20409521 has 4 divisors (see below), whose sum is σ = 22264944. Its totient is φ = 18554100.

The previous prime is 20409511. The next prime is 20409523. The reversal of 20409521 is 12590402.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20409521 - 2¹⁸ = 20147377 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20409523) 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, 927695 + ... + 927716.

It is an arithmetic number, because the mean of its divisors is an integer number (5566236).

Almost surely, 2^20409521 is an apocalyptic number.

It is an amenable number.

20409521 is a deficient number, since it is larger than the sum of its proper divisors (1855423).

20409521 is a wasteful number, since it uses less digits than its factorization.

20409521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1855422.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 20409521 is about 4517.6897857201. The cubic root of 20409521 is about 273.2819433759.

Adding to 20409521 its reverse (12590402), we get a palindrome (32999923).

The spelling of 20409521 in words is "twenty million, four hundred nine thousand, five hundred twenty-one".