21665728671 has 8 divisors (see below), whose sum is σ = 30408040320. Its totient is φ = 13683618072.

The previous prime is 21665728631. The next prime is 21665728771. The reversal of 21665728671 is 17682756612.

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

It is not a de Polignac number, because 21665728671 - 2⁶ = 21665728607 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665728631) 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, 190050195 + ... + 190050308.

It is an arithmetic number, because the mean of its divisors is an integer number (3801005040).

Almost surely, 2^21665728671 is an apocalyptic number.

21665728671 is a deficient number, since it is larger than the sum of its proper divisors (8742311649).

21665728671 is a wasteful number, since it uses less digits than its factorization.

21665728671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 380100525.

The product of its digits is 1693440, while the sum is 51.

The spelling of 21665728671 in words is "twenty-one billion, six hundred sixty-five million, seven hundred twenty-eight thousand, six hundred seventy-one".