21724171 has 16 divisors (see below), whose sum is σ = 25401600. Its totient is φ = 18196128.

The previous prime is 21724169. The next prime is 21724187. The reversal of 21724171 is 17142712.

It is a cyclic number.

It is not a de Polignac number, because 21724171 - 2¹ = 21724169 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21724111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 80625 + ... + 80893.

It is an arithmetic number, because the mean of its divisors is an integer number (1587600).

Almost surely, 2^21724171 is an apocalyptic number.

21724171 is a deficient number, since it is larger than the sum of its proper divisors (3677429).

21724171 is a wasteful number, since it uses less digits than its factorization.

21724171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 498.

The product of its digits is 784, while the sum is 25.

The square root of 21724171 is about 4660.9195444676. The cubic root of 21724171 is about 279.0279687450.

Adding to 21724171 its reverse (17142712), we get a palindrome (38866883).

The spelling of 21724171 in words is "twenty-one million, seven hundred twenty-four thousand, one hundred seventy-one".