21633521 has 12 divisors (see below), whose sum is σ = 26773632. Its totient is φ = 17115696.

The previous prime is 21633499. The next prime is 21633529. The reversal of 21633521 is 12533612.

It is not a de Polignac number, because 21633521 - 2¹⁰ = 21632497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21633529) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7961 + ... + 10326.

It is an arithmetic number, because the mean of its divisors is an integer number (2231136).

Almost surely, 2^21633521 is an apocalyptic number.

It is an amenable number.

21633521 is a deficient number, since it is larger than the sum of its proper divisors (5140111).

21633521 is a wasteful number, since it uses less digits than its factorization.

21633521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18320 (or 18307 counting only the distinct ones).

The product of its digits is 1080, while the sum is 23.

The square root of 21633521 is about 4651.1849027963. The cubic root of 21633521 is about 278.6393210183.

Subtracting from 21633521 its reverse (12533612), we obtain a palindrome (9099909).

The spelling of 21633521 in words is "twenty-one million, six hundred thirty-three thousand, five hundred twenty-one".