181405561 has 4 divisors (see below), whose sum is σ = 186308452. Its totient is φ = 176502672.

The previous prime is 181405537. The next prime is 181405573. The reversal of 181405561 is 165504181.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165504181 = 167 ⋅991043.

It can be written as a sum of positive squares in 2 ways, for example, as 132963961 + 48441600 = 11531^2 + 6960^2 .

It is a cyclic number.

It is not a de Polignac number, because 181405561 - 2⁵ = 181405529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (181402561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2451390 + ... + 2451463.

It is an arithmetic number, because the mean of its divisors is an integer number (46577113).

Almost surely, 2^181405561 is an apocalyptic number.

It is an amenable number.

181405561 is a deficient number, since it is larger than the sum of its proper divisors (4902891).

181405561 is an equidigital number, since it uses as much as digits as its factorization.

181405561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4902890.

The product of its (nonzero) digits is 4800, while the sum is 31.

The square root of 181405561 is about 13468.6881692316. The cubic root of 181405561 is about 566.0874568832.

The spelling of 181405561 in words is "one hundred eighty-one million, four hundred five thousand, five hundred sixty-one".