181997581 has 2 divisors, whose sum is σ = 181997582. Its totient is φ = 181997580.

The previous prime is 181997579. The next prime is 181997609. The reversal of 181997581 is 185799181.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 180472356 + 1525225 = 13434^2 + 1235^2 .

It is an emirp because it is prime and its reverse (185799181) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 181997581 - 2¹ = 181997579 is a prime.

It is a super-2 number, since 2×181997581² = 66246238979703122, which contains 22 as substring.

Together with 181997579, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (181997281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 90998790 + 90998791.

It is an arithmetic number, because the mean of its divisors is an integer number (90998791).

Almost surely, 2^181997581 is an apocalyptic number.

It is an amenable number.

181997581 is a deficient number, since it is larger than the sum of its proper divisors (1).

181997581 is an equidigital number, since it uses as much as digits as its factorization.

181997581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 181440, while the sum is 49.

The square root of 181997581 is about 13490.6479088293. The cubic root of 181997581 is about 566.7026000666.

The spelling of 181997581 in words is "one hundred eighty-one million, nine hundred ninety-seven thousand, five hundred eighty-one".