21042645 has 48 divisors (see below), whose sum is σ = 38072832. Its totient is φ = 9855360.

The previous prime is 21042629. The next prime is 21042647. The reversal of 21042645 is 54624012.

It is not a de Polignac number, because 21042645 - 2⁴ = 21042629 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 (21042647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 356626 + ... + 356684.

It is an arithmetic number, because the mean of its divisors is an integer number (793184).

Almost surely, 2^21042645 is an apocalyptic number.

It is an amenable number.

21042645 is a deficient number, since it is larger than the sum of its proper divisors (17030187).

21042645 is a wasteful number, since it uses less digits than its factorization.

21042645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 170 (or 111 counting only the distinct ones).

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

The square root of 21042645 is about 4587.2262861123. The cubic root of 21042645 is about 276.0790442579.

Adding to 21042645 its reverse (54624012), we get a palindrome (75666657).

The spelling of 21042645 in words is "twenty-one million, forty-two thousand, six hundred forty-five".