21204621 has 6 divisors (see below), whose sum is σ = 30628910. Its totient is φ = 14136408.

The previous prime is 21204619. The next prime is 21204641. The reversal of 21204621 is 12640212.

21204621 is a `hidden beast` number, since 21 + 20 + 4 + 621 = 666.

It can be written as a sum of positive squares in only one way, i.e., 13286025 + 7918596 = 3645^2 + 2814^2 .

It is not a de Polignac number, because 21204621 - 2¹ = 21204619 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21204594 and 21204603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21204641) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1178026 + ... + 1178043.

Almost surely, 2^21204621 is an apocalyptic number.

It is an amenable number.

21204621 is a deficient number, since it is larger than the sum of its proper divisors (9424289).

21204621 is a wasteful number, since it uses less digits than its factorization.

21204621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2356075 (or 2356072 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21204621 is about 4604.8475544800. The cubic root of 21204621 is about 276.7856082834.

Adding to 21204621 its reverse (12640212), we get a palindrome (33844833).

The spelling of 21204621 in words is "twenty-one million, two hundred four thousand, six hundred twenty-one".