20505021 has 4 divisors (see below), whose sum is σ = 27340032. Its totient is φ = 13670012.

The previous prime is 20505007. The next prime is 20505031. The reversal of 20505021 is 12050502.

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 20505021 - 2⁹ = 20504509 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20505031) 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, 3417501 + ... + 3417506.

It is an arithmetic number, because the mean of its divisors is an integer number (6835008).

Almost surely, 2^20505021 is an apocalyptic number.

It is an amenable number.

20505021 is a deficient number, since it is larger than the sum of its proper divisors (6835011).

20505021 is an equidigital number, since it uses as much as digits as its factorization.

20505021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6835010.

The product of its (nonzero) digits is 100, while the sum is 15.

The square root of 20505021 is about 4528.2470118137. The cubic root of 20505021 is about 273.7075261974.

Adding to 20505021 its reverse (12050502), we get a palindrome (32555523).

The spelling of 20505021 in words is "twenty million, five hundred five thousand, twenty-one".