21321818 has 16 divisors (see below), whose sum is σ = 37152384. Its totient is φ = 8987760.

The previous prime is 21321809. The next prime is 21321821. The reversal of 21321818 is 81812312.

It is a Curzon number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 11630 + ... + 13337.

It is an arithmetic number, because the mean of its divisors is an integer number (2322024).

Almost surely, 2^21321818 is an apocalyptic number.

21321818 is a deficient number, since it is larger than the sum of its proper divisors (15830566).

21321818 is a wasteful number, since it uses less digits than its factorization.

21321818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25037.

The product of its digits is 768, while the sum is 26.

The square root of 21321818 is about 4617.5554138527. Note that the first 3 decimals coincide. The cubic root of 21321818 is about 277.2945989702.

The spelling of 21321818 in words is "twenty-one million, three hundred twenty-one thousand, eight hundred eighteen".