21881779 has 4 divisors (see below), whose sum is σ = 21896784. Its totient is φ = 21866776.

The previous prime is 21881773. The next prime is 21881789. The reversal of 21881779 is 97718812.

It is a happy number.

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-21881779 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21881773) 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, 5047 + ... + 8320.

It is an arithmetic number, because the mean of its divisors is an integer number (5474196).

Almost surely, 2^21881779 is an apocalyptic number.

21881779 is a deficient number, since it is larger than the sum of its proper divisors (15005).

21881779 is a wasteful number, since it uses less digits than its factorization.

21881779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15004.

The product of its digits is 56448, while the sum is 43.

The square root of 21881779 is about 4677.7963829136. The cubic root of 21881779 is about 279.7011224121.

The spelling of 21881779 in words is "twenty-one million, eight hundred eighty-one thousand, seven hundred seventy-nine".