21778423 has 4 divisors (see below), whose sum is σ = 21989968. Its totient is φ = 21566880.

The previous prime is 21778409. The next prime is 21778433. The reversal of 21778423 is 32487712.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21778423 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21778433) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 105618 + ... + 105823.

It is an arithmetic number, because the mean of its divisors is an integer number (5497492).

Almost surely, 2^21778423 is an apocalyptic number.

21778423 is a deficient number, since it is larger than the sum of its proper divisors (211545).

21778423 is a wasteful number, since it uses less digits than its factorization.

21778423 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 211544.

The product of its digits is 18816, while the sum is 34.

The square root of 21778423 is about 4666.7357971070. The cubic root of 21778423 is about 279.2600488173.

It can be divided in two parts, 21778 and 423, that added together give a square (22201 = 149²).

The spelling of 21778423 in words is "twenty-one million, seven hundred seventy-eight thousand, four hundred twenty-three".