21025021 has 2 divisors, whose sum is σ = 21025022. Its totient is φ = 21025020.

The previous prime is 21025019. The next prime is 21025031. The reversal of 21025021 is 12052012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20602521 + 422500 = 4539^2 + 650^2 .

It is a cyclic number.

It is not a de Polignac number, because 21025021 - 2¹ = 21025019 is a prime.

Together with 21025019, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21024992 and 21025010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21025031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10512510 + 10512511.

It is an arithmetic number, because the mean of its divisors is an integer number (10512511).

Almost surely, 2^21025021 is an apocalyptic number.

It is an amenable number.

21025021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21025021 is an equidigital number, since it uses as much as digits as its factorization.

21025021 is an evil number, because the sum of its binary digits is even.

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

The square root of 21025021 is about 4585.3048971688. The cubic root of 21025021 is about 276.0019472312.

Adding to 21025021 its reverse (12052012), we get a palindrome (33077033).

The spelling of 21025021 in words is "twenty-one million, twenty-five thousand, twenty-one".