821865 has 32 divisors (see below), whose sum is σ = 1524096. Its totient is φ = 373760.

The previous prime is 821861. The next prime is 821869. The reversal of 821865 is 568128.

It is an interprime number because it is at equal distance from previous prime (821861) and next prime (821869).

It is not a de Polignac number, because 821865 - 2² = 821861 is a prime.

821865 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (821861) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2659 + ... + 2951.

It is an arithmetic number, because the mean of its divisors is an integer number (47628).

2⁸²¹⁸⁶⁵ is an apocalyptic number.

821865 is a gapful number since it is divisible by the number (85) formed by its first and last digit.

It is an amenable number.

821865 is a deficient number, since it is larger than the sum of its proper divisors (702231).

821865 is a wasteful number, since it uses less digits than its factorization.

821865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 329.

The product of its digits is 3840, while the sum is 30.

The square root of 821865 is about 906.5677029323. The cubic root of 821865 is about 93.6699227320.

The spelling of 821865 in words is "eight hundred twenty-one thousand, eight hundred sixty-five".