20521021 has 4 divisors (see below), whose sum is σ = 20533500. Its totient is φ = 20508544.

The previous prime is 20521013. The next prime is 20521043. The reversal of 20521021 is 12012502.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12012502 = 2 ⋅6006251.

It can be written as a sum of positive squares in 2 ways, for example, as 16564900 + 3956121 = 4070^2 + 1989^2 .

It is a cyclic number.

It is not a de Polignac number, because 20521021 - 2³ = 20521013 is a prime.

It is a super-2 number, since 2×20521021² = 842224605764882, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20520992 and 20521010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20521001) 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 3 ways as a sum of consecutive naturals, for example, 3316 + ... + 7213.

It is an arithmetic number, because the mean of its divisors is an integer number (5133375).

Almost surely, 2^20521021 is an apocalyptic number.

It is an amenable number.

20521021 is a deficient number, since it is larger than the sum of its proper divisors (12479).

20521021 is a wasteful number, since it uses less digits than its factorization.

20521021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12478.

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 20521021 is about 4530.0133553887. The cubic root of 20521021 is about 273.7786987142.

Adding to 20521021 its reverse (12012502), we get a palindrome (32533523).

The spelling of 20521021 in words is "twenty million, five hundred twenty-one thousand, twenty-one".