181620016561 has 9 divisors (see below), whose sum is σ = 182514653793. Its totient is φ = 180729749520.

The previous prime is 181620016559. The next prime is 181620016577. The reversal of 181620016561 is 165610026181.

The square root of 181620016561 is 426169.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 9627338161 + 171992678400 = 98119^2 + 414720^2 .

It is not a de Polignac number, because 181620016561 - 2¹ = 181620016559 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 181620016561.

It is not an unprimeable number, because it can be changed into a prime (181620016861) 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 in 8 ways as a sum of consecutive naturals, for example, 97591771 + ... + 97593631.

It is an arithmetic number, because the mean of its divisors is an integer number (20279405977).

Almost surely, 2^181620016561 is an apocalyptic number.

181620016561 is the 426169-th square number.

181620016561 is the 213085-th centered octagonal number.

It is an amenable number.

181620016561 is a deficient number, since it is larger than the sum of its proper divisors (894637232).

181620016561 is an frugal number, since it uses more digits than its factorization.

181620016561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4180 (or 2090 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 37.

The spelling of 181620016561 in words is "one hundred eighty-one billion, six hundred twenty million, sixteen thousand, five hundred sixty-one".