181531993 has 2 divisors, whose sum is σ = 181531994. Its totient is φ = 181531992.

The previous prime is 181531963. The next prime is 181531997. The reversal of 181531993 is 399135181.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 176278729 + 5253264 = 13277^2 + 2292^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-181531993 is a prime.

It is not a weakly prime, because it can be changed into another prime (181531997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 90765996 + 90765997.

It is an arithmetic number, because the mean of its divisors is an integer number (90765997).

Almost surely, 2^181531993 is an apocalyptic number.

It is an amenable number.

181531993 is a deficient number, since it is larger than the sum of its proper divisors (1).

181531993 is an equidigital number, since it uses as much as digits as its factorization.

181531993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 29160, while the sum is 40.

The square root of 181531993 is about 13473.3809045837. The cubic root of 181531993 is about 566.2189393433.

The spelling of 181531993 in words is "one hundred eighty-one million, five hundred thirty-one thousand, nine hundred ninety-three".