21806818 has 32 divisors (see below), whose sum is σ = 38102400. Its totient is φ = 9250560.

The previous prime is 21806803. The next prime is 21806819. The reversal of 21806818 is 81860812.

It is a super-2 number, since 2×21806818² = 951074622570248, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (34).

It is not an unprimeable number, because it can be changed into a prime (21806819) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 74280 + ... + 74572.

It is an arithmetic number, because the mean of its divisors is an integer number (1190700).

Almost surely, 2^21806818 is an apocalyptic number.

21806818 is a deficient number, since it is larger than the sum of its proper divisors (16295582).

21806818 is a wasteful number, since it uses less digits than its factorization.

21806818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 522.

The product of its (nonzero) digits is 6144, while the sum is 34.

The square root of 21806818 is about 4669.7770824741. Note that the first 3 decimals coincide. The cubic root of 21806818 is about 279.3813637743.

It can be divided in two parts, 2180 and 6818, that added together give a palindrome (8998).

The spelling of 21806818 in words is "twenty-one million, eight hundred six thousand, eight hundred eighteen".