21204481 has 4 divisors (see below), whose sum is σ = 21935700. Its totient is φ = 20473264.

The previous prime is 21204451. The next prime is 21204487. The reversal of 21204481 is 18440212.

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 8179600 + 13024881 = 2860^2 + 3609^2 .

It is a cyclic number.

It is not a de Polignac number, because 21204481 - 2¹⁵ = 21171713 is a prime.

It is a super-2 number, since 2×21204481² = 899260028958722, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21204487) 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, 365566 + ... + 365623.

It is an arithmetic number, because the mean of its divisors is an integer number (5483925).

Almost surely, 2^21204481 is an apocalyptic number.

It is an amenable number.

21204481 is a deficient number, since it is larger than the sum of its proper divisors (731219).

21204481 is an equidigital number, since it uses as much as digits as its factorization.

21204481 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 731218.

The product of its (nonzero) digits is 512, while the sum is 22.

The square root of 21204481 is about 4604.8323530830. The cubic root of 21204481 is about 276.7849991383.

Adding to 21204481 its reverse (18440212), we get a palindrome (39644693).

The spelling of 21204481 in words is "twenty-one million, two hundred four thousand, four hundred eighty-one".