21791818 has 16 divisors (see below), whose sum is σ = 34020000. Its totient is φ = 10456432.

The previous prime is 21791797. The next prime is 21791821. The reversal of 21791818 is 81819712.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9333 + ... + 11431.

It is an arithmetic number, because the mean of its divisors is an integer number (2126250).

Almost surely, 2^21791818 is an apocalyptic number.

21791818 is a deficient number, since it is larger than the sum of its proper divisors (12228182).

21791818 is a wasteful number, since it uses less digits than its factorization.

21791818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2309.

The product of its digits is 8064, while the sum is 37.

The square root of 21791818 is about 4668.1707338100. The cubic root of 21791818 is about 279.3172908209.

The spelling of 21791818 in words is "twenty-one million, seven hundred ninety-one thousand, eight hundred eighteen".