166855171721 has 4 divisors (see below), whose sum is σ = 190691624832. Its totient is φ = 143018718612.

The previous prime is 166855171633. The next prime is 166855171727. The reversal of 166855171721 is 127171558661.

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.

It is a de Polignac number, because none of the positive numbers 2^k-166855171721 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 166855171721.

It is not an unprimeable number, because it can be changed into a prime (166855171727) 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, 11918226545 + ... + 11918226558.

It is an arithmetic number, because the mean of its divisors is an integer number (47672906208).

Almost surely, 2^166855171721 is an apocalyptic number.

It is an amenable number.

166855171721 is a deficient number, since it is larger than the sum of its proper divisors (23836453111).

166855171721 is an equidigital number, since it uses as much as digits as its factorization.

166855171721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23836453110.

The product of its digits is 705600, while the sum is 50.

The spelling of 166855171721 in words is "one hundred sixty-six billion, eight hundred fifty-five million, one hundred seventy-one thousand, seven hundred twenty-one".