181620991 has 4 divisors (see below), whose sum is σ = 181792912. Its totient is φ = 181449072.

The previous prime is 181620977. The next prime is 181621001. The reversal of 181620991 is 199026181.

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

It is a cyclic number.

It is not a de Polignac number, because 181620991 - 2⁹ = 181620479 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 181620991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (181620961) 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 3 ways as a sum of consecutive naturals, for example, 84366 + ... + 86491.

It is an arithmetic number, because the mean of its divisors is an integer number (45448228).

Almost surely, 2^181620991 is an apocalyptic number.

181620991 is a deficient number, since it is larger than the sum of its proper divisors (171921).

181620991 is a wasteful number, since it uses less digits than its factorization.

181620991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171920.

The product of its (nonzero) digits is 7776, while the sum is 37.

The square root of 181620991 is about 13476.6832343867. The cubic root of 181620991 is about 566.3114558551.

The spelling of 181620991 in words is "one hundred eighty-one million, six hundred twenty thousand, nine hundred ninety-one".