181505981 has 2 divisors, whose sum is σ = 181505982. Its totient is φ = 181505980.

The previous prime is 181505969. The next prime is 181506001. The reversal of 181505981 is 189505181.

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., 143880025 + 37625956 = 11995^2 + 6134^2 .

It is a cyclic number.

It is not a de Polignac number, because 181505981 - 2¹⁰ = 181504957 is a prime.

It is a super-2 number, since 2×181505981² = 65888842277544722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (181507981) 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 as a sum of consecutive naturals, namely, 90752990 + 90752991.

It is an arithmetic number, because the mean of its divisors is an integer number (90752991).

Almost surely, 2^181505981 is an apocalyptic number.

It is an amenable number.

181505981 is a deficient number, since it is larger than the sum of its proper divisors (1).

181505981 is an equidigital number, since it uses as much as digits as its factorization.

181505981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14400, while the sum is 38.

The square root of 181505981 is about 13472.4155592084. The cubic root of 181505981 is about 566.1918932557.

The spelling of 181505981 in words is "one hundred eighty-one million, five hundred five thousand, nine hundred eighty-one".