21043021 has 2 divisors, whose sum is σ = 21043022. Its totient is φ = 21043020.

The previous prime is 21043019. The next prime is 21043027. The reversal of 21043021 is 12034012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18369796 + 2673225 = 4286^2 + 1635^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043021 - 2¹ = 21043019 is a prime.

Together with 21043019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21042992 and 21043010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21043027) 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 as a sum of consecutive naturals, namely, 10521510 + 10521511.

It is an arithmetic number, because the mean of its divisors is an integer number (10521511).

Almost surely, 2^21043021 is an apocalyptic number.

It is an amenable number.

21043021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21043021 is an equidigital number, since it uses as much as digits as its factorization.

21043021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21043021 is about 4587.2672693010. The cubic root of 21043021 is about 276.0806886187.

Adding to 21043021 its reverse (12034012), we get a palindrome (33077033).

Subtracting from 21043021 its reverse (12034012), we obtain a palindrome (9009009).

The spelling of 21043021 in words is "twenty-one million, forty-three thousand, twenty-one".