2181981 has 4 divisors (see below), whose sum is σ = 2909312. Its totient is φ = 1454652.

The previous prime is 2181973. The next prime is 2182007. The reversal of 2181981 is 1891812.

2181981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 2181981 - 2³ = 2181973 is a prime.

It is a super-2 number, since 2×2181981² = 9522082168722, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2181581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 363661 + ... + 363666.

It is an arithmetic number, because the mean of its divisors is an integer number (727328).

2^2181981 is an apocalyptic number.

It is an amenable number.

2181981 is a deficient number, since it is larger than the sum of its proper divisors (727331).

2181981 is an equidigital number, since it uses as much as digits as its factorization.

2181981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 727330.

The product of its digits is 1152, while the sum is 30.

The square root of 2181981 is about 1477.1530049389. The cubic root of 2181981 is about 129.7030896535.

The spelling of 2181981 in words is "two million, one hundred eighty-one thousand, nine hundred eighty-one".