21806990 has 32 divisors (see below), whose sum is σ = 41679360. Its totient is φ = 8197024.

The previous prime is 21806989. The next prime is 21807007. The reversal of 21806990 is 9960812.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21806990.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12767 + ... + 14373.

It is an arithmetic number, because the mean of its divisors is an integer number (1302480).

Almost surely, 2^21806990 is an apocalyptic number.

21806990 is a deficient number, since it is larger than the sum of its proper divisors (19872370).

21806990 is a wasteful number, since it uses less digits than its factorization.

21806990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1696.

The product of its (nonzero) digits is 7776, while the sum is 35.

The square root of 21806990 is about 4669.7954987344. The cubic root of 21806990 is about 279.3820983070.

The spelling of 21806990 in words is "twenty-one million, eight hundred six thousand, nine hundred ninety".