817921 has 8 divisors (see below), whose sum is σ = 932904. Its totient is φ = 710400.

The previous prime is 817919. The next prime is 817933. The reversal of 817921 is 129718.

817921 = 639² + 640².

It can be written as a sum of positive squares in 4 ways, for example, as 69696 + 748225 = 264^2 + 865^2 .

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 817921 - 2¹ = 817919 is a prime.

It is a Duffinian number.

817921 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 817921.

It is not an unprimeable number, because it can be changed into a prime (817951) 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, 1630 + ... + 2071.

It is an arithmetic number, because the mean of its divisors is an integer number (116613).

2⁸¹⁷⁹²¹ is an apocalyptic number.

817921 is the 640-th centered square number.

It is an amenable number.

817921 is a deficient number, since it is larger than the sum of its proper divisors (114983).

817921 is a wasteful number, since it uses less digits than its factorization.

817921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3731.

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

The square root of 817921 is about 904.3898495671. The cubic root of 817921 is about 93.5198467025.

It can be divided in two parts, 81 and 7921, that multiplied together give a square (641601 = 801²).

The spelling of 817921 in words is "eight hundred seventeen thousand, nine hundred twenty-one".