1817981821 has 4 divisors (see below), whose sum is σ = 1860260512. Its totient is φ = 1775703132.

The previous prime is 1817981777. The next prime is 1817981831. The reversal of 1817981821 is 1281897181.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1281897181 = 4583 ⋅279707.

It is a cyclic number.

It is not a de Polignac number, because 1817981821 - 2¹³ = 1817973629 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 (1817981831) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21139281 + ... + 21139366.

It is an arithmetic number, because the mean of its divisors is an integer number (465065128).

Almost surely, 2^1817981821 is an apocalyptic number.

It is an amenable number.

1817981821 is a deficient number, since it is larger than the sum of its proper divisors (42278691).

1817981821 is an equidigital number, since it uses as much as digits as its factorization.

1817981821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42278690.

The product of its digits is 64512, while the sum is 46.

The square root of 1817981821 is about 42637.7980317933. The cubic root of 1817981821 is about 1220.4776909703.

It can be divided in two parts, 18179 and 81821, that added together give a 5-th power (100000 = 10⁵).

The spelling of 1817981821 in words is "one billion, eight hundred seventeen million, nine hundred eighty-one thousand, eight hundred twenty-one".