820861 has 4 divisors (see below), whose sum is σ = 840924. Its totient is φ = 800800.

The previous prime is 820837. The next prime is 820873. The reversal of 820861 is 168028.

820861 = 121² + 122² + ... + 161².

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 37636 + 783225 = 194^2 + 885^2 .

It is a cyclic number.

It is not a de Polignac number, because 820861 - 2⁷ = 820733 is a prime.

It is a Duffinian number.

820861 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (820891) 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 3 ways as a sum of consecutive naturals, for example, 9970 + ... + 10051.

It is an arithmetic number, because the mean of its divisors is an integer number (210231).

2⁸²⁰⁸⁶¹ is an apocalyptic number.

It is an amenable number.

820861 is a deficient number, since it is larger than the sum of its proper divisors (20063).

820861 is a wasteful number, since it uses less digits than its factorization.

820861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20062.

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

The square root of 820861 is about 906.0137968044. The cubic root of 820861 is about 93.6317644279.

Subtracting from 820861 its sum of digits (25), we obtain a square (820836 = 906²).

Adding to 820861 its reverse (168028), we get a palindrome (988889).

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

The spelling of 820861 in words is "eight hundred twenty thousand, eight hundred sixty-one".