21242021 has 4 divisors (see below), whose sum is σ = 21252000. Its totient is φ = 21232044.

The previous prime is 21241991. The next prime is 21242047. The reversal of 21242021 is 12024212.

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 21242021 - 2¹⁸ = 20979877 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21241987 and 21242005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21242521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 371 + ... + 6528.

It is an arithmetic number, because the mean of its divisors is an integer number (5313000).

Almost surely, 2^21242021 is an apocalyptic number.

It is an amenable number.

21242021 is a deficient number, since it is larger than the sum of its proper divisors (9979).

21242021 is an equidigital number, since it uses as much as digits as its factorization.

21242021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9978.

The product of its (nonzero) digits is 64, while the sum is 14.

The square root of 21242021 is about 4608.9067033300. The cubic root of 21242021 is about 276.9482410992.

Adding to 21242021 its reverse (12024212), we get a palindrome (33266233).

The spelling of 21242021 in words is "twenty-one million, two hundred forty-two thousand, twenty-one".