21105818 has 4 divisors (see below), whose sum is σ = 31658730. Its totient is φ = 10552908.

The previous prime is 21105811. The next prime is 21105863. The reversal of 21105818 is 81850112.

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., 17330569 + 3775249 = 4163^2 + 1943^2 .

It is not an unprimeable number, because it can be changed into a prime (21105811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5276453 + ... + 5276456.

Almost surely, 2^21105818 is an apocalyptic number.

21105818 is a deficient number, since it is larger than the sum of its proper divisors (10552912).

21105818 is a wasteful number, since it uses less digits than its factorization.

21105818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10552911.

The product of its (nonzero) digits is 640, while the sum is 26.

The square root of 21105818 is about 4594.1068772940. The cubic root of 21105818 is about 276.3550443729.

The spelling of 21105818 in words is "twenty-one million, one hundred five thousand, eight hundred eighteen".