921721 has 4 divisors (see below), whose sum is σ = 944244. Its totient is φ = 899200.

The previous prime is 921703. The next prime is 921733. The reversal of 921721 is 127129.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127129 = 19 ⋅6691.

It can be written as a sum of positive squares in 2 ways, for example, as 40000 + 881721 = 200^2 + 939^2 .

It is a cyclic number.

It is not a de Polignac number, because 921721 - 2¹⁷ = 790649 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 921692 and 921701.

It is not an unprimeable number, because it can be changed into a prime (921751) 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, 11200 + ... + 11281.

It is an arithmetic number, because the mean of its divisors is an integer number (236061).

2⁹²¹⁷²¹ is an apocalyptic number.

It is an amenable number.

921721 is a deficient number, since it is larger than the sum of its proper divisors (22523).

921721 is a wasteful number, since it uses less digits than its factorization.

921721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22522.

The product of its digits is 252, while the sum is 22.

The square root of 921721 is about 960.0630187649. The cubic root of 921721 is about 97.3194906921.

The spelling of 921721 in words is "nine hundred twenty-one thousand, seven hundred twenty-one".