2181781 has 4 divisors (see below), whose sum is σ = 2493472. Its totient is φ = 1870092.

The previous prime is 2181737. The next prime is 2181833. The reversal of 2181781 is 1871812.

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 2181781 - 2²¹ = 84629 is a prime.

It is a super-2 number, since 2×2181781² = 9520336663922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2181731) 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, 155835 + ... + 155848.

It is an arithmetic number, because the mean of its divisors is an integer number (623368).

2^2181781 is an apocalyptic number.

It is an amenable number.

2181781 is a deficient number, since it is larger than the sum of its proper divisors (311691).

2181781 is an equidigital number, since it uses as much as digits as its factorization.

2181781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311690.

The product of its digits is 896, while the sum is 28.

The square root of 2181781 is about 1477.0853055934. The cubic root of 2181781 is about 129.6991266781.

The spelling of 2181781 in words is "two million, one hundred eighty-one thousand, seven hundred eighty-one".