1665981865 has 4 divisors (see below), whose sum is σ = 1999178244. Its totient is φ = 1332785488.

The previous prime is 1665981853. The next prime is 1665981899. The reversal of 1665981865 is 5681895661.

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 340439401 + 1325542464 = 18451^2 + 36408^2 .

It is a cyclic number.

It is not a de Polignac number, because 1665981865 - 2²¹ = 1663884713 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 166598182 + ... + 166598191.

It is an arithmetic number, because the mean of its divisors is an integer number (499794561).

Almost surely, 2^1665981865 is an apocalyptic number.

It is an amenable number.

1665981865 is a deficient number, since it is larger than the sum of its proper divisors (333196379).

1665981865 is an equidigital number, since it uses as much as digits as its factorization.

1665981865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333196378.

The product of its digits is 3110400, while the sum is 55.

The square root of 1665981865 is about 40816.4411113953. The cubic root of 1665981865 is about 1185.4686948205.

The spelling of 1665981865 in words is "one billion, six hundred sixty-five million, nine hundred eighty-one thousand, eight hundred sixty-five".