21840123 has 4 divisors (see below), whose sum is σ = 29120168. Its totient is φ = 14560080.

The previous prime is 21840109. The next prime is 21840131. The reversal of 21840123 is 32104812.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 21840123 - 2¹⁰ = 21839099 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21840123.

It is not an unprimeable number, because it can be changed into a prime (21840193) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3640018 + ... + 3640023.

It is an arithmetic number, because the mean of its divisors is an integer number (7280042).

Almost surely, 2^21840123 is an apocalyptic number.

21840123 is a deficient number, since it is larger than the sum of its proper divisors (7280045).

21840123 is an equidigital number, since it uses as much as digits as its factorization.

21840123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7280044.

The product of its (nonzero) digits is 384, while the sum is 21.

The square root of 21840123 is about 4673.3417379858. The cubic root of 21840123 is about 279.5235221173.

Adding to 21840123 its reverse (32104812), we get a palindrome (53944935).

The spelling of 21840123 in words is "twenty-one million, eight hundred forty thousand, one hundred twenty-three".