821821 has 16 divisors (see below), whose sum is σ = 1104768. Its totient is φ = 590400.

The previous prime is 821819. The next prime is 821827. The reversal of 821821 is 128128.

821821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 821821 - 2¹ = 821819 is a prime.

It is a zygodrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 821792 and 821801.

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 15 ways as a sum of consecutive naturals, for example, 591 + ... + 1411.

It is an arithmetic number, because the mean of its divisors is an integer number (69048).

2⁸²¹⁸²¹ is an apocalyptic number.

It is an amenable number.

821821 is a deficient number, since it is larger than the sum of its proper divisors (282947).

821821 is a wasteful number, since it uses less digits than its factorization.

821821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 852.

The product of its digits is 256, while the sum is 22.

The square root of 821821 is about 906.5434352528. The cubic root of 821821 is about 93.6682511070.

Adding to 821821 its reverse (128128), we get a palindrome (949949).

It can be divided in two parts, 8218 and 21, that multiplied together give a triangular number (172578 = T₅₈₇).

The spelling of 821821 in words is "eight hundred twenty-one thousand, eight hundred twenty-one".