21824281 has 4 divisors (see below), whose sum is σ = 21879652. Its totient is φ = 21768912.

The previous prime is 21824261. The next prime is 21824291. The reversal of 21824281 is 18242812.

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 11964681 + 9859600 = 3459^2 + 3140^2 .

It is a cyclic number.

It is not a de Polignac number, because 21824281 - 2⁵ = 21824249 is a prime.

It is a super-2 number, since 2×21824281² = 952598482333922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21824221) 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, 27090 + ... + 27883.

It is an arithmetic number, because the mean of its divisors is an integer number (5469913).

Almost surely, 2^21824281 is an apocalyptic number.

It is an amenable number.

21824281 is a deficient number, since it is larger than the sum of its proper divisors (55371).

21824281 is an equidigital number, since it uses as much as digits as its factorization.

21824281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55370.

The product of its digits is 2048, while the sum is 28.

The square root of 21824281 is about 4671.6464977564. The cubic root of 21824281 is about 279.4559205024.

The spelling of 21824281 in words is "twenty-one million, eight hundred twenty-four thousand, two hundred eighty-one".