1821805 has 8 divisors (see below), whose sum is σ = 2314872. Its totient is φ = 1371648.

The previous prime is 1821791. The next prime is 1821821. The reversal of 1821805 is 5081281.

It can be written as a sum of positive squares in 4 ways, for example, as 84681 + 1737124 = 291^2 + 1318^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1821805 - 2¹¹ = 1819757 is a prime.

It is a Duffinian number.

1821805 is a lucky number.

It is a plaindrome in base 14.

It is a self number, because there is not a number n which added to its sum of digits gives 1821805.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10632 + ... + 10801.

It is an arithmetic number, because the mean of its divisors is an integer number (289359).

2^1821805 is an apocalyptic number.

It is an amenable number.

1821805 is a deficient number, since it is larger than the sum of its proper divisors (493067).

1821805 is a wasteful number, since it uses less digits than its factorization.

1821805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21455.

The product of its (nonzero) digits is 640, while the sum is 25.

The square root of 1821805 is about 1349.7425680477. The cubic root of 1821805 is about 122.1332638571.

The spelling of 1821805 in words is "one million, eight hundred twenty-one thousand, eight hundred five".