181366991 has 8 divisors (see below), whose sum is σ = 199861200. Its totient is φ = 163521792.

The previous prime is 181366973. The next prime is 181366993. The reversal of 181366991 is 199663181.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 181366991 - 2²⁶ = 114258127 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 (181366993) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 161666 + ... + 162783.

It is an arithmetic number, because the mean of its divisors is an integer number (24982650).

Almost surely, 2^181366991 is an apocalyptic number.

181366991 is a deficient number, since it is larger than the sum of its proper divisors (18494209).

181366991 is a wasteful number, since it uses less digits than its factorization.

181366991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 324505.

The product of its digits is 69984, while the sum is 44.

The square root of 181366991 is about 13467.2562535952. The cubic root of 181366991 is about 566.0473340029.

The spelling of 181366991 in words is "one hundred eighty-one million, three hundred sixty-six thousand, nine hundred ninety-one".