871821 has 12 divisors (see below), whose sum is σ = 1269372. Its totient is φ = 576576.

The previous prime is 871817. The next prime is 871823. The reversal of 871821 is 128178.

It can be written as a sum of positive squares in 2 ways, for example, as 114921 + 756900 = 339^2 + 870^2 .

It is not a de Polignac number, because 871821 - 2² = 871817 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (871823) 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 in 11 ways as a sum of consecutive naturals, for example, 1105 + ... + 1721.

It is an arithmetic number, because the mean of its divisors is an integer number (105781).

2⁸⁷¹⁸²¹ is an apocalyptic number.

It is an amenable number.

871821 is a deficient number, since it is larger than the sum of its proper divisors (397551).

871821 is a wasteful number, since it uses less digits than its factorization.

871821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 780 (or 777 counting only the distinct ones).

The product of its digits is 896, while the sum is 27.

The square root of 871821 is about 933.7135535056. The cubic root of 871821 is about 95.5305860384.

Adding to 871821 its reverse (128178), we get a palindrome (999999).

The spelling of 871821 in words is "eight hundred seventy-one thousand, eight hundred twenty-one".