20051021 has 4 divisors (see below), whose sum is σ = 20060832. Its totient is φ = 20041212.

The previous prime is 20050981. The next prime is 20051047. The reversal of 20051021 is 12015002.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20051021 - 2⁶ = 20050957 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20050993 and 20051011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20051071) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 551 + ... + 6356.

It is an arithmetic number, because the mean of its divisors is an integer number (5015208).

Almost surely, 2^20051021 is an apocalyptic number.

It is an amenable number.

20051021 is a deficient number, since it is larger than the sum of its proper divisors (9811).

20051021 is an equidigital number, since it uses as much as digits as its factorization.

20051021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9810.

The product of its (nonzero) digits is 20, while the sum is 11.

The square root of 20051021 is about 4477.8366428444. The cubic root of 20051021 is about 271.6723861610.

Adding to 20051021 its reverse (12015002), we get a palindrome (32066023).

The spelling of 20051021 in words is "twenty million, fifty-one thousand, twenty-one".