21778123 has 4 divisors (see below), whose sum is σ = 22924360. Its totient is φ = 20631888.

The previous prime is 21778117. The next prime is 21778157. The reversal of 21778123 is 32187712.

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

It is a cyclic number.

It is not a de Polignac number, because 21778123 - 2¹³ = 21769931 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21778193) 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, 573090 + ... + 573127.

It is an arithmetic number, because the mean of its divisors is an integer number (5731090).

Almost surely, 2^21778123 is an apocalyptic number.

21778123 is a deficient number, since it is larger than the sum of its proper divisors (1146237).

21778123 is a wasteful number, since it uses less digits than its factorization.

21778123 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1146236.

The product of its digits is 4704, while the sum is 31.

The square root of 21778123 is about 4666.7036546153. The cubic root of 21778123 is about 279.2587665329.

The spelling of 21778123 in words is "twenty-one million, seven hundred seventy-eight thousand, one hundred twenty-three".