21665415779 has 8 divisors (see below), whose sum is σ = 26063658240. Its totient is φ = 17592969096.

The previous prime is 21665415773. The next prime is 21665415781. The reversal of 21665415779 is 97751456612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21665415779 - 2⁴ = 21665415763 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21665415779.

It is not an unprimeable number, because it can be changed into a prime (21665415773) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 81448799 + ... + 81449064.

It is an arithmetic number, because the mean of its divisors is an integer number (3257957280).

Almost surely, 2^21665415779 is an apocalyptic number.

21665415779 is a deficient number, since it is larger than the sum of its proper divisors (4398242461).

21665415779 is a wasteful number, since it uses less digits than its factorization.

21665415779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 162897889.

The product of its digits is 3175200, while the sum is 53.

The spelling of 21665415779 in words is "twenty-one billion, six hundred sixty-five million, four hundred fifteen thousand, seven hundred seventy-nine".