170661721 has 4 divisors (see below), whose sum is σ = 174824244. Its totient is φ = 166499200.

The previous prime is 170661709. The next prime is 170661731. The reversal of 170661721 is 127166071.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127166071 = 1559 ⋅81569.

It can be written as a sum of positive squares in 2 ways, for example, as 52722121 + 117939600 = 7261^2 + 10860^2 .

It is a cyclic number.

It is not a de Polignac number, because 170661721 - 2⁷ = 170661593 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (170661731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2081200 + ... + 2081281.

It is an arithmetic number, because the mean of its divisors is an integer number (43706061).

Almost surely, 2^170661721 is an apocalyptic number.

It is an amenable number.

170661721 is a deficient number, since it is larger than the sum of its proper divisors (4162523).

170661721 is an equidigital number, since it uses as much as digits as its factorization.

170661721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4162522.

The product of its (nonzero) digits is 3528, while the sum is 31.

The square root of 170661721 is about 13063.7560066009. The cubic root of 170661721 is about 554.6836614073.

The spelling of 170661721 in words is "one hundred seventy million, six hundred sixty-one thousand, seven hundred twenty-one".