21642779 has 4 divisors (see below), whose sum is σ = 21659184. Its totient is φ = 21626376.

The previous prime is 21642773. The next prime is 21642791. The reversal of 21642779 is 97724612.

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 21642779 - 2⁴ = 21642763 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21642773) 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, 6032 + ... + 8925.

It is an arithmetic number, because the mean of its divisors is an integer number (5414796).

Almost surely, 2^21642779 is an apocalyptic number.

21642779 is a deficient number, since it is larger than the sum of its proper divisors (16405).

21642779 is a wasteful number, since it uses less digits than its factorization.

21642779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16404.

The product of its digits is 42336, while the sum is 38.

The square root of 21642779 is about 4652.1800266112. The cubic root of 21642779 is about 278.6790629684.

The spelling of 21642779 in words is "twenty-one million, six hundred forty-two thousand, seven hundred seventy-nine".