81820 has 12 divisors (see below), whose sum is σ = 171864. Its totient is φ = 32720.

The previous prime is 81817. The next prime is 81839. The reversal of 81820 is 2818.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 2026 + ... + 2065.

It is an arithmetic number, because the mean of its divisors is an integer number (14322).

2⁸¹⁸²⁰ is an apocalyptic number.

It is an amenable number.

81820 is an abundant number, since it is smaller than the sum of its proper divisors (90044).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (85932).

81820 is a wasteful number, since it uses less digits than its factorization.

81820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4100 (or 4098 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 19.

The square root of 81820 is about 286.0419549647. The cubic root of 81820 is about 43.4130026802.

It can be divided in two parts, 818 and 20, that added together give a palindrome (838).

The spelling of 81820 in words is "eighty-one thousand, eight hundred twenty".