21721441 has 4 divisors (see below), whose sum is σ = 24824512. Its totient is φ = 18618372.

The previous prime is 21721409. The next prime is 21721457. The reversal of 21721441 is 14412712.

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 21721441 - 2⁵ = 21721409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21721741) 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, 1551525 + ... + 1551538.

It is an arithmetic number, because the mean of its divisors is an integer number (6206128).

Almost surely, 2^21721441 is an apocalyptic number.

It is an amenable number.

21721441 is a deficient number, since it is larger than the sum of its proper divisors (3103071).

21721441 is an equidigital number, since it uses as much as digits as its factorization.

21721441 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3103070.

The product of its digits is 448, while the sum is 22.

The square root of 21721441 is about 4660.6266746007. The cubic root of 21721441 is about 279.0162801016.

The spelling of 21721441 in words is "twenty-one million, seven hundred twenty-one thousand, four hundred forty-one".