21251724 has 48 divisors (see below), whose sum is σ = 55732992. Its totient is φ = 6253632.

The previous prime is 21251719. The next prime is 21251731. The reversal of 21251724 is 42715212.

It is a plaindrome in base 16.

It is a junction number, because it is equal to n+sod(n) for n = 21251694 and 21251703.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 627 + ... + 6549.

It is an arithmetic number, because the mean of its divisors is an integer number (1161104).

Almost surely, 2^21251724 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21251724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27866496).

21251724 is an abundant number, since it is smaller than the sum of its proper divisors (34481268).

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

21251724 is a wasteful number, since it uses less digits than its factorization.

21251724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5966 (or 5964 counting only the distinct ones).

The product of its digits is 1120, while the sum is 24.

The square root of 21251724 is about 4609.9592189086. The cubic root of 21251724 is about 276.9904031221.

Adding to 21251724 its reverse (42715212), we get a palindrome (63966936).

The spelling of 21251724 in words is "twenty-one million, two hundred fifty-one thousand, seven hundred twenty-four".