861820 has 24 divisors (see below), whose sum is σ = 1855728. Its totient is φ = 336000.

The previous prime is 861803. The next prime is 861823. The reversal of 861820 is 28168.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (861823) 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 7 ways as a sum of consecutive naturals, for example, 295 + ... + 1345.

It is an arithmetic number, because the mean of its divisors is an integer number (77322).

2⁸⁶¹⁸²⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 861820, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (927864).

861820 is an abundant number, since it is smaller than the sum of its proper divisors (993908).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

861820 is a wasteful number, since it uses less digits than its factorization.

861820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1101 (or 1099 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 861820 is about 928.3426091697. The cubic root of 861820 is about 95.1638906908.

Adding to 861820 its reverse (28168), we get a palindrome (889988).

It can be divided in two parts, 861 and 820, that added together give a square (1681 = 41²).

The spelling of 861820 in words is "eight hundred sixty-one thousand, eight hundred twenty".