21872123 has 8 divisors (see below), whose sum is σ = 26919648. Its totient is φ = 17305344.

The previous prime is 21872113. The next prime is 21872159. The reversal of 21872123 is 32127812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21872123 - 2⁴ = 21872107 is a prime.

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 = 21872092 and 21872101.

It is not an unprimeable number, because it can be changed into a prime (21872113) 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, 120086 + ... + 120267.

It is an arithmetic number, because the mean of its divisors is an integer number (3364956).

Almost surely, 2^21872123 is an apocalyptic number.

21872123 is a deficient number, since it is larger than the sum of its proper divisors (5047525).

21872123 is a wasteful number, since it uses less digits than its factorization.

21872123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240373.

The product of its digits is 1344, while the sum is 26.

The square root of 21872123 is about 4676.7641591169. The cubic root of 21872123 is about 279.6599741520.

Adding to 21872123 its reverse (32127812), we get a palindrome (53999935).

The spelling of 21872123 in words is "twenty-one million, eight hundred seventy-two thousand, one hundred twenty-three".