20021021 has 2 divisors, whose sum is σ = 20021022. Its totient is φ = 20021020.

The previous prime is 20020943. The next prime is 20021059. The reversal of 20021021 is 12012002.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 1651225 = 4286^2 + 1285^2 .

It is a cyclic number.

It is not a de Polignac number, because 20021021 - 2²² = 15826717 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20021081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10010510 + 10010511.

It is an arithmetic number, because the mean of its divisors is an integer number (10010511).

Almost surely, 2^20021021 is an apocalyptic number.

It is an amenable number.

20021021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20021021 is an equidigital number, since it uses as much as digits as its factorization.

20021021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8, while the sum is 8.

The square root of 20021021 is about 4474.4855570222. The cubic root of 20021021 is about 271.5368279820.

Adding to 20021021 its reverse (12012002), we get a palindrome (32033023).

The spelling of 20021021 in words is "twenty million, twenty-one thousand, twenty-one".