891721 has 8 divisors (see below), whose sum is σ = 934920. Its totient is φ = 849408.

The previous prime is 891707. The next prime is 891743. The reversal of 891721 is 127198.

It can be written as a sum of positive squares in 4 ways, for example, as 10000 + 881721 = 100^2 + 939^2 .

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 891721 - 2⁷ = 891593 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 891721.

It is not an unprimeable number, because it can be changed into a prime (891421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2655 + ... + 2971.

It is an arithmetic number, because the mean of its divisors is an integer number (116865).

2⁸⁹¹⁷²¹ is an apocalyptic number.

It is an amenable number.

891721 is a deficient number, since it is larger than the sum of its proper divisors (43199).

891721 is a wasteful number, since it uses less digits than its factorization.

891721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 443.

The product of its digits is 1008, while the sum is 28.

The square root of 891721 is about 944.3098008599. The cubic root of 891721 is about 96.2519783705.

It can be divided in two parts, 891 and 721, that multiplied together give a triangular number (642411 = T₁₁₃₃).

The spelling of 891721 in words is "eight hundred ninety-one thousand, seven hundred twenty-one".