181811821 has 8 divisors (see below), whose sum is σ = 197710200. Its totient is φ = 166491648.

The previous prime is 181811813. The next prime is 181811827. The reversal of 181811821 is 128118181.

It can be written as a sum of positive squares in 4 ways, for example, as 78057225 + 103754596 = 8835^2 + 10186^2 .

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 181811821 - 2³ = 181811813 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 (181811827) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 143896 + ... + 145153.

It is an arithmetic number, because the mean of its divisors is an integer number (24713775).

Almost surely, 2^181811821 is an apocalyptic number.

It is an amenable number.

181811821 is a deficient number, since it is larger than the sum of its proper divisors (15898379).

181811821 is a wasteful number, since it uses less digits than its factorization.

181811821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 289103.

The product of its digits is 1024, while the sum is 31.

The square root of 181811821 is about 13483.7613817510. The cubic root of 181811821 is about 566.5097284354.

It can be divided in two parts, 18181 and 1821, that added together give a palindrome (20002).

The spelling of 181811821 in words is "one hundred eighty-one million, eight hundred eleven thousand, eight hundred twenty-one".