2181511821 has 4 divisors (see below), whose sum is σ = 2908682432. Its totient is φ = 1454341212.

The previous prime is 2181511817. The next prime is 2181511883. The reversal of 2181511821 is 1281151812.

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.

It is not a de Polignac number, because 2181511821 - 2² = 2181511817 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 (2181511811) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 363585301 + ... + 363585306.

It is an arithmetic number, because the mean of its divisors is an integer number (727170608).

Almost surely, 2^2181511821 is an apocalyptic number.

It is an amenable number.

2181511821 is a deficient number, since it is larger than the sum of its proper divisors (727170611).

2181511821 is an equidigital number, since it uses as much as digits as its factorization.

2181511821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 727170610.

The product of its digits is 1280, while the sum is 30.

The square root of 2181511821 is about 46706.6571379284. The cubic root of 2181511821 is about 1296.9379254713.

The spelling of 2181511821 in words is "two billion, one hundred eighty-one million, five hundred eleven thousand, eight hundred twenty-one".