21806218 has 16 divisors (see below), whose sum is σ = 37497600. Its totient is φ = 9316656.

The previous prime is 21806207. The next prime is 21806227. The reversal of 21806218 is 81260812.

It is a super-2 number, since 2×21806218² = 951022286927048, which contains 22 as substring.

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, 2655 + ... + 7117.

It is an arithmetic number, because the mean of its divisors is an integer number (2343600).

Almost surely, 2^21806218 is an apocalyptic number.

21806218 is a deficient number, since it is larger than the sum of its proper divisors (15691382).

21806218 is a wasteful number, since it uses less digits than its factorization.

21806218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4821.

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 21806218 is about 4669.7128391369. The cubic root of 21806218 is about 279.3788014203.

The spelling of 21806218 in words is "twenty-one million, eight hundred six thousand, two hundred eighteen".