1812905821 has 4 divisors (see below), whose sum is σ = 1813806652. Its totient is φ = 1812004992.

The previous prime is 1812905819. The next prime is 1812905827. The reversal of 1812905821 is 1285092181.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1285092181 = 97 ⋅13248373.

It can be written as a sum of positive squares in 2 ways, for example, as 1639035225 + 173870596 = 40485^2 + 13186^2 .

It is a cyclic number.

It is not a de Polignac number, because 1812905821 - 2¹ = 1812905819 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1812905827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 447390 + ... + 451423.

It is an arithmetic number, because the mean of its divisors is an integer number (453451663).

Almost surely, 2^1812905821 is an apocalyptic number.

It is an amenable number.

1812905821 is a deficient number, since it is larger than the sum of its proper divisors (900831).

1812905821 is an equidigital number, since it uses as much as digits as its factorization.

1812905821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 900830.

The product of its (nonzero) digits is 11520, while the sum is 37.

The square root of 1812905821 is about 42578.2317739946. The cubic root of 1812905821 is about 1219.3407306545.

The spelling of 1812905821 in words is "one billion, eight hundred twelve million, nine hundred five thousand, eight hundred twenty-one".