21204645 has 48 divisors (see below), whose sum is σ = 42645120. Its totient is φ = 8807040.

The previous prime is 21204641. The next prime is 21204679. The reversal of 21204645 is 54640212.

It is not a de Polignac number, because 21204645 - 2² = 21204641 is a prime.

It is a Curzon number.

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 47 ways as a sum of consecutive naturals, for example, 11871 + ... + 13539.

It is an arithmetic number, because the mean of its divisors is an integer number (888440).

Almost surely, 2^21204645 is an apocalyptic number.

It is an amenable number.

21204645 is an abundant number, since it is smaller than the sum of its proper divisors (21440475).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21204645 is a wasteful number, since it uses less digits than its factorization.

21204645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1706 (or 1695 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21204645 is about 4604.8501604287. The cubic root of 21204645 is about 276.7857127080.

Adding to 21204645 its reverse (54640212), we get a palindrome (75844857).

The spelling of 21204645 in words is "twenty-one million, two hundred four thousand, six hundred forty-five".