21404521 has 4 divisors (see below), whose sum is σ = 21420544. Its totient is φ = 21388500.

The previous prime is 21404503. The next prime is 21404531. The reversal of 21404521 is 12540412.

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 21404521 - 2¹⁷ = 21273449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21404531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5805 + ... + 8746.

It is an arithmetic number, because the mean of its divisors is an integer number (5355136).

Almost surely, 2^21404521 is an apocalyptic number.

It is an amenable number.

21404521 is a deficient number, since it is larger than the sum of its proper divisors (16023).

21404521 is a wasteful number, since it uses less digits than its factorization.

21404521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16022.

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21404521 is about 4626.5020263694. The cubic root of 21404521 is about 277.6526595572.

Adding to 21404521 its reverse (12540412), we get a palindrome (33944933).

The spelling of 21404521 in words is "twenty-one million, four hundred four thousand, five hundred twenty-one".