21724251 has 8 divisors (see below), whose sum is σ = 28987200. Its totient is φ = 14472072.

The previous prime is 21724243. The next prime is 21724271. The reversal of 21724251 is 15242712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21724251 - 2³ = 21724243 is a prime.

It is a super-2 number, since 2×21724251² = 943886163022002, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21724231) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6700 + ... + 9398.

It is an arithmetic number, because the mean of its divisors is an integer number (3623400).

Almost surely, 2^21724251 is an apocalyptic number.

21724251 is a deficient number, since it is larger than the sum of its proper divisors (7262949).

21724251 is a wasteful number, since it uses less digits than its factorization.

21724251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5385.

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

The square root of 21724251 is about 4660.9281264572. The cubic root of 21724251 is about 279.0283112546.

Adding to 21724251 its reverse (15242712), we get a palindrome (36966963).

The spelling of 21724251 in words is "twenty-one million, seven hundred twenty-four thousand, two hundred fifty-one".