21090645 has 16 divisors (see below), whose sum is σ = 37494720. Its totient is φ = 11248272.

The previous prime is 21090631. The next prime is 21090647. The reversal of 21090645 is 54609012.

21090645 is a `hidden beast` number, since 2 + 10 + 9 + 0 + 645 = 666.

It is not a de Polignac number, because 21090645 - 2¹⁵ = 21057877 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21090647) 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 15 ways as a sum of consecutive naturals, for example, 77979 + ... + 78248.

It is an arithmetic number, because the mean of its divisors is an integer number (2343420).

Almost surely, 2^21090645 is an apocalyptic number.

It is an amenable number.

21090645 is a deficient number, since it is larger than the sum of its proper divisors (16404075).

21090645 is a wasteful number, since it uses less digits than its factorization.

21090645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 156241 (or 156235 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21090645 is about 4592.4552256936. The cubic root of 21090645 is about 276.2888044969.

Adding to 21090645 its reverse (54609012), we get a palindrome (75699657).

The spelling of 21090645 in words is "twenty-one million, ninety thousand, six hundred forty-five".