817721 has 2 divisors, whose sum is σ = 817722. Its totient is φ = 817720.

The previous prime is 817711. The next prime is 817723. The reversal of 817721 is 127718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 657721 + 160000 = 811^2 + 400^2 .

It is a cyclic number.

It is not a de Polignac number, because 817721 - 2¹⁴ = 801337 is a prime.

Together with 817723, it forms a pair of twin primes.

It is a Chen prime.

It is a plaindrome in base 15.

It is not a weakly prime, because it can be changed into another prime (817723) 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 as a sum of consecutive naturals, namely, 408860 + 408861.

It is an arithmetic number, because the mean of its divisors is an integer number (408861).

2⁸¹⁷⁷²¹ is an apocalyptic number.

It is an amenable number.

817721 is a deficient number, since it is larger than the sum of its proper divisors (1).

817721 is an equidigital number, since it uses as much as digits as its factorization.

817721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 784, while the sum is 26.

The square root of 817721 is about 904.2792710220. The cubic root of 817721 is about 93.5122235156.

The spelling of 817721 in words is "eight hundred seventeen thousand, seven hundred twenty-one".