21720841 has 4 divisors (see below), whose sum is σ = 21748500. Its totient is φ = 21693184.

The previous prime is 21720833. The next prime is 21720877. The reversal of 21720841 is 14802712.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 12988816 + 8732025 = 3604^2 + 2955^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720841 - 2³ = 21720833 is a prime.

It is a Duffinian number.

It is a plaindrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (21720821) 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, 12616 + ... + 14233.

It is an arithmetic number, because the mean of its divisors is an integer number (5437125).

Almost surely, 2^21720841 is an apocalyptic number.

It is an amenable number.

21720841 is a deficient number, since it is larger than the sum of its proper divisors (27659).

21720841 is an equidigital number, since it uses as much as digits as its factorization.

21720841 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27658.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21720841 is about 4660.5623051301. The cubic root of 21720841 is about 279.0137110377.

The spelling of 21720841 in words is "twenty-one million, seven hundred twenty thousand, eight hundred forty-one".