21878123 has 2 divisors, whose sum is σ = 21878124. Its totient is φ = 21878122.

The previous prime is 21878111. The next prime is 21878149. The reversal of 21878123 is 32187812.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21878123 - 2¹⁰ = 21877099 is a prime.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21878123.

It is not a weakly prime, because it can be changed into another prime (21874123) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10939061 + 10939062.

It is an arithmetic number, because the mean of its divisors is an integer number (10939062).

Almost surely, 2^21878123 is an apocalyptic number.

21878123 is a deficient number, since it is larger than the sum of its proper divisors (1).

21878123 is an equidigital number, since it uses as much as digits as its factorization.

21878123 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 21878123 is about 4677.4055842956. The cubic root of 21878123 is about 279.6855440892.

The spelling of 21878123 in words is "twenty-one million, eight hundred seventy-eight thousand, one hundred twenty-three".