161665521 has 16 divisors (see below), whose sum is σ = 218880000. Its totient is φ = 106121808.

The previous prime is 161665513. The next prime is 161665523. The reversal of 161665521 is 125566161.

161665521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 161665521 - 2³ = 161665513 is a prime.

It is a super-2 number, since 2×161665521² = 52271481360402882, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161665523) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 117580 + ... + 118946.

It is an arithmetic number, because the mean of its divisors is an integer number (13680000).

Almost surely, 2^161665521 is an apocalyptic number.

It is an amenable number.

161665521 is a deficient number, since it is larger than the sum of its proper divisors (57214479).

161665521 is a wasteful number, since it uses less digits than its factorization.

161665521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1948.

The product of its digits is 10800, while the sum is 33.

The square root of 161665521 is about 12714.7756960160. The cubic root of 161665521 is about 544.7607411480.

The spelling of 161665521 in words is "one hundred sixty-one million, six hundred sixty-five thousand, five hundred twenty-one".