161728021 has 16 divisors (see below), whose sum is σ = 210760704. Its totient is φ = 120432384.

The previous prime is 161728013. The next prime is 161728033. The reversal of 161728021 is 120827161.

It is a cyclic number.

It is not a de Polignac number, because 161728021 - 2³ = 161728013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161728001) 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 15 ways as a sum of consecutive naturals, for example, 50725 + ... + 53818.

It is an arithmetic number, because the mean of its divisors is an integer number (13172544).

Almost surely, 2^161728021 is an apocalyptic number.

It is an amenable number.

161728021 is a deficient number, since it is larger than the sum of its proper divisors (49032683).

161728021 is a wasteful number, since it uses less digits than its factorization.

161728021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 104580.

The product of its (nonzero) digits is 1344, while the sum is 28.

The square root of 161728021 is about 12717.2332289693. The cubic root of 161728021 is about 544.8309337272.

It can be divided in two parts, 1617280 and 21, that added together give a triangular number (1617301 = T₁₇₉₈).

The spelling of 161728021 in words is "one hundred sixty-one million, seven hundred twenty-eight thousand, twenty-one".