164520721 has 4 divisors (see below), whose sum is σ = 167217844. Its totient is φ = 161823600.

The previous prime is 164520701. The next prime is 164520731. The reversal of 164520721 is 127025461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127025461 = 71 ⋅1789091.

It can be written as a sum of positive squares in 2 ways, for example, as 33189121 + 131331600 = 5761^2 + 11460^2 .

It is a cyclic number.

It is not a de Polignac number, because 164520721 - 2⁷ = 164520593 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 164520721.

It is not an unprimeable number, because it can be changed into a prime (164520701) 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, 1348470 + ... + 1348591.

It is an arithmetic number, because the mean of its divisors is an integer number (41804461).

Almost surely, 2^164520721 is an apocalyptic number.

It is an amenable number.

164520721 is a deficient number, since it is larger than the sum of its proper divisors (2697123).

164520721 is an equidigital number, since it uses as much as digits as its factorization.

164520721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2697122.

The product of its (nonzero) digits is 3360, while the sum is 28.

The square root of 164520721 is about 12826.5631016262. The cubic root of 164520721 is about 547.9490790858.

It can be divided in two parts, 1645 and 20721, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 164520721 in words is "one hundred sixty-four million, five hundred twenty thousand, seven hundred twenty-one".