21721252 has 24 divisors (see below), whose sum is σ = 43762880. Its totient is φ = 9240480.

The previous prime is 21721247. The next prime is 21721253. The reversal of 21721252 is 25212712.

It is not an unprimeable number, because it can be changed into a prime (21721253) 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 7 ways as a sum of consecutive naturals, for example, 1102 + ... + 6682.

Almost surely, 2^21721252 is an apocalyptic number.

It is an amenable number.

21721252 is an abundant number, since it is smaller than the sum of its proper divisors (22041628).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21721252 is a wasteful number, since it uses less digits than its factorization.

21721252 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5731 (or 5729 counting only the distinct ones).

The product of its digits is 560, while the sum is 22.

The square root of 21721252 is about 4660.6063983134. The cubic root of 21721252 is about 279.0154708515.

Adding to 21721252 its reverse (25212712), we get a palindrome (46933964).

The spelling of 21721252 in words is "twenty-one million, seven hundred twenty-one thousand, two hundred fifty-two".