21645818 has 4 divisors (see below), whose sum is σ = 32468730. Its totient is φ = 10822908.

The previous prime is 21645817. The next prime is 21645859. The reversal of 21645818 is 81854612.

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

It can be written as a sum of positive squares in only one way, i.e., 11992369 + 9653449 = 3463^2 + 3107^2 .

It is not an unprimeable number, because it can be changed into a prime (21645817) 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 as a sum of consecutive naturals, namely, 5411453 + ... + 5411456.

Almost surely, 2^21645818 is an apocalyptic number.

21645818 is a deficient number, since it is larger than the sum of its proper divisors (10822912).

21645818 is a wasteful number, since it uses less digits than its factorization.

21645818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10822911.

The product of its digits is 15360, while the sum is 35.

The square root of 21645818 is about 4652.5066362124. The cubic root of 21645818 is about 278.6921060568.

The spelling of 21645818 in words is "twenty-one million, six hundred forty-five thousand, eight hundred eighteen".