17991661 has 16 divisors (see below), whose sum is σ = 19813248. Its totient is φ = 16268800.

The previous prime is 17991641. The next prime is 17991679. The reversal of 17991661 is 16619971.

It is not a de Polignac number, because 17991661 - 2¹⁵ = 17958893 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 (17991641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 57696 + ... + 58006.

It is an arithmetic number, because the mean of its divisors is an integer number (1238328).

Almost surely, 2^17991661 is an apocalyptic number.

It is an amenable number.

17991661 is a deficient number, since it is larger than the sum of its proper divisors (1821587).

17991661 is a wasteful number, since it uses less digits than its factorization.

17991661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 452.

The product of its digits is 20412, while the sum is 40.

The square root of 17991661 is about 4241.6578126954. The cubic root of 17991661 is about 262.0336621279.

The spelling of 17991661 in words is "seventeen million, nine hundred ninety-one thousand, six hundred sixty-one".