181522721 has 4 divisors (see below), whose sum is σ = 184947732. Its totient is φ = 178097712.

The previous prime is 181522711. The next prime is 181522723. The reversal of 181522721 is 127225181.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127225181 = 59 ⋅2156359.

It can be written as a sum of positive squares in 2 ways, for example, as 44890000 + 136632721 = 6700^2 + 11689^2 .

It is a cyclic number.

It is not a de Polignac number, because 181522721 - 2¹⁴ = 181506337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (181522723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1712426 + ... + 1712531.

It is an arithmetic number, because the mean of its divisors is an integer number (46236933).

Almost surely, 2^181522721 is an apocalyptic number.

It is an amenable number.

181522721 is a deficient number, since it is larger than the sum of its proper divisors (3425011).

181522721 is an equidigital number, since it uses as much as digits as its factorization.

181522721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3425010.

The product of its digits is 2240, while the sum is 29.

The square root of 181522721 is about 13473.0368143192. The cubic root of 181522721 is about 566.2092990383.

The spelling of 181522721 in words is "one hundred eighty-one million, five hundred twenty-two thousand, seven hundred twenty-one".