821820 has 24 divisors (see below), whose sum is σ = 2301264. Its totient is φ = 219136.

The previous prime is 821819. The next prime is 821827. The reversal of 821820 is 28128.

It is a super-2 number, since 2×821820² = 1350776224800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6789 + ... + 6908.

It is an arithmetic number, because the mean of its divisors is an integer number (95886).

2⁸²¹⁸²⁰ is an apocalyptic number.

It is an amenable number.

821820 is an abundant number, since it is smaller than the sum of its proper divisors (1479444).

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

821820 is a wasteful number, since it uses less digits than its factorization.

821820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13709 (or 13707 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 21.

The square root of 821820 is about 906.5428837071. The cubic root of 821820 is about 93.6682131149.

Adding to 821820 its reverse (28128), we get a palindrome (849948).

The spelling of 821820 in words is "eight hundred twenty-one thousand, eight hundred twenty".