1668181909 has 4 divisors (see below), whose sum is σ = 1668273516. Its totient is φ = 1668090304.

The previous prime is 1668181901. The next prime is 1668181961. The reversal of 1668181909 is 9091818661.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 9091818661 = 157 ⋅57909673.

It can be written as a sum of positive squares in 2 ways, for example, as 1242915025 + 425266884 = 35255^2 + 20622^2 .

It is a cyclic number.

It is not a de Polignac number, because 1668181909 - 2³ = 1668181901 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 (1668181901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8194 + ... + 58339.

It is an arithmetic number, because the mean of its divisors is an integer number (417068379).

Almost surely, 2^1668181909 is an apocalyptic number.

It is an amenable number.

1668181909 is a deficient number, since it is larger than the sum of its proper divisors (91607).

1668181909 is an equidigital number, since it uses as much as digits as its factorization.

1668181909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91606.

The product of its (nonzero) digits is 186624, while the sum is 49.

The square root of 1668181909 is about 40843.3826831226. The cubic root of 1668181909 is about 1185.9902963526.

The spelling of 1668181909 in words is "one billion, six hundred sixty-eight million, one hundred eighty-one thousand, nine hundred nine".