1820821 has 2 divisors, whose sum is σ = 1820822. Its totient is φ = 1820820.

The previous prime is 1820813. The next prime is 1820837. The reversal of 1820821 is 1280281.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1311025 + 509796 = 1145^2 + 714^2 .

It is an emirp because it is prime and its reverse (1280281) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1820821 - 2³ = 1820813 is a prime.

It is a super-2 number, since 2×1820821² = 6630778228082, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 1820792 and 1820801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1820891) 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 as a sum of consecutive naturals, namely, 910410 + 910411.

It is an arithmetic number, because the mean of its divisors is an integer number (910411).

2^1820821 is an apocalyptic number.

It is an amenable number.

1820821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1820821 is an equidigital number, since it uses as much as digits as its factorization.

1820821 is an odious number, because the sum of its binary digits is odd.

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

The square root of 1820821 is about 1349.3780048600. The cubic root of 1820821 is about 122.1112708748. Note that the first 3 decimals are identical.

The spelling of 1820821 in words is "one million, eight hundred twenty thousand, eight hundred twenty-one".