21861818 has 16 divisors (see below), whose sum is σ = 37657440. Its totient is φ = 9414000.

The previous prime is 21861817. The next prime is 21861839. The reversal of 21861818 is 81816812.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21861817) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 25733 + ... + 26568.

It is an arithmetic number, because the mean of its divisors is an integer number (2353590).

Almost surely, 2^21861818 is an apocalyptic number.

21861818 is a deficient number, since it is larger than the sum of its proper divisors (15795622).

21861818 is a wasteful number, since it uses less digits than its factorization.

21861818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 52333.

The product of its digits is 6144, while the sum is 35.

The square root of 21861818 is about 4675.6623060268. The cubic root of 21861818 is about 279.6160468699.

It can be divided in two parts, 2186 and 1818, that added together give a palindrome (4004).

The spelling of 21861818 in words is "twenty-one million, eight hundred sixty-one thousand, eight hundred eighteen".