21304021 has 4 divisors (see below), whose sum is σ = 21503232. Its totient is φ = 21104812.

The previous prime is 21304001. The next prime is 21304027. The reversal of 21304021 is 12040312.

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.

It is a cyclic number.

It is not a de Polignac number, because 21304021 - 2¹³ = 21295829 is a prime.

It is a super-2 number, since 2×21304021² = 907722621536882, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21303992 and 21304010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21304027) 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 in 3 ways as a sum of consecutive naturals, for example, 99445 + ... + 99658.

It is an arithmetic number, because the mean of its divisors is an integer number (5375808).

Almost surely, 2^21304021 is an apocalyptic number.

It is an amenable number.

21304021 is a deficient number, since it is larger than the sum of its proper divisors (199211).

21304021 is a wasteful number, since it uses less digits than its factorization.

21304021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 199210.

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

The square root of 21304021 is about 4615.6279096132. The cubic root of 21304021 is about 277.2174262876.

Adding to 21304021 its reverse (12040312), we get a palindrome (33344333).

The spelling of 21304021 in words is "twenty-one million, three hundred four thousand, twenty-one".