2181357781 has 4 divisors (see below), whose sum is σ = 2182142700. Its totient is φ = 2180572864.

The previous prime is 2181357767. The next prime is 2181357797. The reversal of 2181357781 is 1877531812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1128355281 + 1053002500 = 33591^2 + 32450^2 .

It is a cyclic number.

It is not a de Polignac number, because 2181357781 - 2¹³ = 2181349589 is a prime.

It is a super-2 number, since 2×2181357781² = 9516643537458487922, 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 (2181307781) 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, 388276 + ... + 393853.

It is an arithmetic number, because the mean of its divisors is an integer number (545535675).

Almost surely, 2^2181357781 is an apocalyptic number.

It is an amenable number.

2181357781 is a deficient number, since it is larger than the sum of its proper divisors (784919).

2181357781 is an equidigital number, since it uses as much as digits as its factorization.

2181357781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 784918.

The product of its digits is 94080, while the sum is 43.

The square root of 2181357781 is about 46705.0080933512. The cubic root of 2181357781 is about 1296.9073984733.

The spelling of 2181357781 in words is "two billion, one hundred eighty-one million, three hundred fifty-seven thousand, seven hundred eighty-one".