21645163 has 4 divisors (see below), whose sum is σ = 21727728. Its totient is φ = 21562600.

The previous prime is 21645133. The next prime is 21645167. The reversal of 21645163 is 36154612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21645163 - 2¹⁷ = 21514091 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21645167) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40888 + ... + 41413.

It is an arithmetic number, because the mean of its divisors is an integer number (5431932).

Almost surely, 2^21645163 is an apocalyptic number.

21645163 is a deficient number, since it is larger than the sum of its proper divisors (82565).

21645163 is an equidigital number, since it uses as much as digits as its factorization.

21645163 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 82564.

The product of its digits is 4320, while the sum is 28.

The square root of 21645163 is about 4652.4362435180. The cubic root of 21645163 is about 278.6892949646.

Adding to 21645163 its reverse (36154612), we get a palindrome (57799775).

The spelling of 21645163 in words is "twenty-one million, six hundred forty-five thousand, one hundred sixty-three".