21238521 has 4 divisors (see below), whose sum is σ = 28318032. Its totient is φ = 14159012.

The previous prime is 21238519. The next prime is 21238543. The reversal of 21238521 is 12583212.

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 21238521 - 2¹ = 21238519 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21238491 and 21238500.

It is not an unprimeable number, because it can be changed into a prime (21238571) 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, 3539751 + ... + 3539756.

It is an arithmetic number, because the mean of its divisors is an integer number (7079508).

Almost surely, 2^21238521 is an apocalyptic number.

It is an amenable number.

21238521 is a deficient number, since it is larger than the sum of its proper divisors (7079511).

21238521 is an equidigital number, since it uses as much as digits as its factorization.

21238521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7079510.

The product of its digits is 960, while the sum is 24.

The square root of 21238521 is about 4608.5269880950. The cubic root of 21238521 is about 276.9330295509.

The spelling of 21238521 in words is "twenty-one million, two hundred thirty-eight thousand, five hundred twenty-one".