2181681 has 8 divisors (see below), whose sum is σ = 3232160. Its totient is φ = 1454436.

The previous prime is 2181671. The next prime is 2181689. The reversal of 2181681 is 1861812.

It is not a de Polignac number, because 2181681 - 2⁵ = 2181649 is a prime.

It is a super-2 number, since 2×2181681² = 9519463971522, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 80803 = 2181681 / (2 + 1 + 8 + 1 + 6 + 8 + 1).

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (2181689) 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, 40375 + ... + 40428.

It is an arithmetic number, because the mean of its divisors is an integer number (404020).

2^2181681 is an apocalyptic number.

It is an amenable number.

2181681 is a deficient number, since it is larger than the sum of its proper divisors (1050479).

2181681 is an equidigital number, since it uses as much as digits as its factorization.

2181681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 80812 (or 80806 counting only the distinct ones).

The product of its digits is 768, while the sum is 27.

The square root of 2181681 is about 1477.0514547571. The cubic root of 2181681 is about 129.6971450997.

The spelling of 2181681 in words is "two million, one hundred eighty-one thousand, six hundred eighty-one".