21721443 has 4 divisors (see below), whose sum is σ = 28961928. Its totient is φ = 14480960.

The previous prime is 21721409. The next prime is 21721457. The reversal of 21721443 is 34412712.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21721443 - 2⁸ = 21721187 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21725443) 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 3 ways as a sum of consecutive naturals, for example, 3620238 + ... + 3620243.

It is an arithmetic number, because the mean of its divisors is an integer number (7240482).

Almost surely, 2^21721443 is an apocalyptic number.

21721443 is a deficient number, since it is larger than the sum of its proper divisors (7240485).

21721443 is an equidigital number, since it uses as much as digits as its factorization.

21721443 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7240484.

The product of its digits is 1344, while the sum is 24.

The square root of 21721443 is about 4660.6268891642. The cubic root of 21721443 is about 279.0162886650.

The spelling of 21721443 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred forty-three".