821005 has 4 divisors (see below), whose sum is σ = 985212. Its totient is φ = 656800.

The previous prime is 821003. The next prime is 821027. The reversal of 821005 is 500128.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 306916 + 514089 = 554^2 + 717^2 .

It is not a de Polignac number, because 821005 - 2¹ = 821003 is a prime.

It is a Duffinian number.

821005 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 821005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821003) 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, 82096 + ... + 82105.

It is an arithmetic number, because the mean of its divisors is an integer number (246303).

2⁸²¹⁰⁰⁵ is an apocalyptic number.

It is an amenable number.

821005 is a deficient number, since it is larger than the sum of its proper divisors (164207).

821005 is a wasteful number, since it uses less digits than its factorization.

821005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 164206.

The product of its (nonzero) digits is 80, while the sum is 16.

The square root of 821005 is about 906.0932623080. The cubic root of 821005 is about 93.6372392426.

The spelling of 821005 in words is "eight hundred twenty-one thousand, five".