821665 has 8 divisors (see below), whose sum is σ = 1061928. Its totient is φ = 606720.

The previous prime is 821663. The next prime is 821677. The reversal of 821665 is 566128.

It can be written as a sum of positive squares in 4 ways, for example, as 54289 + 767376 = 233^2 + 876^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 821665 - 2¹ = 821663 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821663) 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, 6256 + ... + 6385.

It is an arithmetic number, because the mean of its divisors is an integer number (132741).

2⁸²¹⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

821665 is a deficient number, since it is larger than the sum of its proper divisors (240263).

821665 is a wasteful number, since it uses less digits than its factorization.

821665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12659.

The product of its digits is 2880, while the sum is 28.

The square root of 821665 is about 906.4573900631. The cubic root of 821665 is about 93.6623239559.

It can be divided in two parts, 8216 and 65, that added together give a square (8281 = 91²).

The spelling of 821665 in words is "eight hundred twenty-one thousand, six hundred sixty-five".