21787028779 has 4 divisors (see below), whose sum is σ = 21791441376. Its totient is φ = 21782616184.

The previous prime is 21787028773. The next prime is 21787028789. The reversal of 21787028779 is 97782078712.

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 21787028779 - 2⁹ = 21787028267 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21787028773) 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, 2198884 + ... + 2208769.

It is an arithmetic number, because the mean of its divisors is an integer number (5447860344).

Almost surely, 2^21787028779 is an apocalyptic number.

21787028779 is a deficient number, since it is larger than the sum of its proper divisors (4412597).

21787028779 is an equidigital number, since it uses as much as digits as its factorization.

21787028779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4412596.

The product of its (nonzero) digits is 5531904, while the sum is 58.

The spelling of 21787028779 in words is "twenty-one billion, seven hundred eighty-seven million, twenty-eight thousand, seven hundred seventy-nine".