166555561 has 4 divisors (see below), whose sum is σ = 166847824. Its totient is φ = 166263300.

The previous prime is 166555553. The next prime is 166555573. The reversal of 166555561 is 165555661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 165555661 = 1381 ⋅119881.

It is a cyclic number.

It is not a de Polignac number, because 166555561 - 2³ = 166555553 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (166555541) 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, 145275 + ... + 146416.

It is an arithmetic number, because the mean of its divisors is an integer number (41711956).

Almost surely, 2^166555561 is an apocalyptic number.

It is an amenable number.

166555561 is a deficient number, since it is larger than the sum of its proper divisors (292263).

166555561 is an equidigital number, since it uses as much as digits as its factorization.

166555561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 292262.

The product of its digits is 135000, while the sum is 40.

The square root of 166555561 is about 12905.6406660034. The cubic root of 166555561 is about 550.1988933559.

The spelling of 166555561 in words is "one hundred sixty-six million, five hundred fifty-five thousand, five hundred sixty-one".