171665561 has 4 divisors (see below), whose sum is σ = 171799824. Its totient is φ = 171531300.

The previous prime is 171665539. The next prime is 171665563. The reversal of 171665561 is 165566171.

171665561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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: 165566171 = 19 ⋅8714009.

It is a cyclic number.

It is not a de Polignac number, because 171665561 - 2¹⁸ = 171403417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (171665563) 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, 65195 + ... + 67776.

It is an arithmetic number, because the mean of its divisors is an integer number (42949956).

Almost surely, 2^171665561 is an apocalyptic number.

It is an amenable number.

171665561 is a deficient number, since it is larger than the sum of its proper divisors (134263).

171665561 is a wasteful number, since it uses less digits than its factorization.

171665561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 134262.

The product of its digits is 37800, while the sum is 38.

The square root of 171665561 is about 13102.1204772357. The cubic root of 171665561 is about 555.7690941621.

The spelling of 171665561 in words is "one hundred seventy-one million, six hundred sixty-five thousand, five hundred sixty-one".