21724817 has 4 divisors (see below), whose sum is σ = 22049136. Its totient is φ = 21400500.

The previous prime is 21724783. The next prime is 21724819. The reversal of 21724817 is 71842712.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21724817 - 2¹⁴ = 21708433 is a prime.

It is a super-3 number, since 3×21724817³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21724819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 162059 + ... + 162192.

It is an arithmetic number, because the mean of its divisors is an integer number (5512284).

Almost surely, 2^21724817 is an apocalyptic number.

It is an amenable number.

21724817 is a deficient number, since it is larger than the sum of its proper divisors (324319).

21724817 is an equidigital number, since it uses as much as digits as its factorization.

21724817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 324318.

The product of its digits is 6272, while the sum is 32.

The square root of 21724817 is about 4660.9888435824. The cubic root of 21724817 is about 279.0307344858.

The spelling of 21724817 in words is "twenty-one million, seven hundred twenty-four thousand, eight hundred seventeen".