21233213521 has 4 divisors (see below), whose sum is σ = 22866537652. Its totient is φ = 19599889392.

The previous prime is 21233213513. The next prime is 21233213527. The reversal of 21233213521 is 12531233212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13394590225 + 7838623296 = 115735^2 + 88536^2 .

It is a cyclic number.

It is not a de Polignac number, because 21233213521 - 2³ = 21233213513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21233213527) 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, 816662046 + ... + 816662071.

It is an arithmetic number, because the mean of its divisors is an integer number (5716634413).

Almost surely, 2^21233213521 is an apocalyptic number.

It is an amenable number.

21233213521 is a deficient number, since it is larger than the sum of its proper divisors (1633324131).

21233213521 is a wasteful number, since it uses less digits than its factorization.

21233213521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1633324130.

The product of its digits is 2160, while the sum is 25.

Adding to 21233213521 its reverse (12531233212), we get a palindrome (33764446733).

The spelling of 21233213521 in words is "twenty-one billion, two hundred thirty-three million, two hundred thirteen thousand, five hundred twenty-one".