91721 has 4 divisors (see below), whose sum is σ = 104832. Its totient is φ = 78612.

The previous prime is 91711. The next prime is 91733. The reversal of 91721 is 12719.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 91721 - 2¹⁰ = 90697 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 91693 and 91702.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 91721.

It is not an unprimeable number, because it can be changed into a prime (91711) 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, 6545 + ... + 6558.

It is an arithmetic number, because the mean of its divisors is an integer number (26208).

2⁹¹⁷²¹ is an apocalyptic number.

It is an amenable number.

91721 is a deficient number, since it is larger than the sum of its proper divisors (13111).

91721 is a wasteful number, since it uses less digits than its factorization.

91721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13110.

The product of its digits is 126, while the sum is 20.

The square root of 91721 is about 302.8547506644. The cubic root of 91721 is about 45.0978938812.

The spelling of 91721 in words is "ninety-one thousand, seven hundred twenty-one".