21816123 has 48 divisors (see below), whose sum is σ = 36443520. Its totient is φ = 11539584.

The previous prime is 21816107. The next prime is 21816163. The reversal of 21816123 is 32161812.

It is not a de Polignac number, because 21816123 - 2⁴ = 21816107 is a prime.

It is a super-2 number, since 2×21816123² = 951886445502258, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a junction number, because it is equal to n+sod(n) for n = 21816093 and 21816102.

It is not an unprimeable number, because it can be changed into a prime (21816103) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 203836 + ... + 203942.

It is an arithmetic number, because the mean of its divisors is an integer number (759240).

Almost surely, 2^21816123 is an apocalyptic number.

21816123 is a deficient number, since it is larger than the sum of its proper divisors (14627397).

21816123 is a wasteful number, since it uses less digits than its factorization.

21816123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 216 (or 209 counting only the distinct ones).

The product of its digits is 576, while the sum is 24.

The square root of 21816123 is about 4670.7732764501. The cubic root of 21816123 is about 279.4210955976.

Adding to 21816123 its reverse (32161812), we get a palindrome (53977935).

The spelling of 21816123 in words is "twenty-one million, eight hundred sixteen thousand, one hundred twenty-three".