166555661 has 2 divisors, whose sum is σ = 166555662. Its totient is φ = 166555660.

The previous prime is 166555651. The next prime is 166555663.

166555661 is nontrivially palindromic in base 10.

166555661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 84290761 + 82264900 = 9181^2 + 9070^2 .

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 166555661 - 2¹⁰ = 166554637 is a prime.

It is a super-2 number, since 2×166555661² = 55481576422293842, which contains 22 as substring.

Together with 166555663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (166555663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 83277830 + 83277831.

It is an arithmetic number, because the mean of its divisors is an integer number (83277831).

Almost surely, 2^166555661 is an apocalyptic number.

It is an amenable number.

166555661 is a deficient number, since it is larger than the sum of its proper divisors (1).

166555661 is an equidigital number, since it uses as much as digits as its factorization.

166555661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 162000, while the sum is 41.

The square root of 166555661 is about 12905.6445402777. The cubic root of 166555661 is about 550.1990034691.

Adding to 166555661 its product of digits (162000), we get a palindrome (166717661).

Subtracting from 166555661 its product of digits (162000), we obtain a palindrome (166393661).

The spelling of 166555661 in words is "one hundred sixty-six million, five hundred fifty-five thousand, six hundred sixty-one".