201665521 has 4 divisors (see below), whose sum is σ = 202198000. Its totient is φ = 201133044.

The previous prime is 201665479. The next prime is 201665531. The reversal of 201665521 is 125566102.

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, and also an emirpimes, since its reverse is a distinct semiprime: 125566102 = 2 ⋅62783051.

It is a cyclic number.

It is not a de Polignac number, because 201665521 - 2²⁵ = 168111089 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 201665521.

It is not an unprimeable number, because it can be changed into a prime (201665531) 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, 265671 + ... + 266428.

It is an arithmetic number, because the mean of its divisors is an integer number (50549500).

Almost surely, 2^201665521 is an apocalyptic number.

It is an amenable number.

201665521 is a deficient number, since it is larger than the sum of its proper divisors (532479).

201665521 is an equidigital number, since it uses as much as digits as its factorization.

201665521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 532478.

The product of its (nonzero) digits is 3600, while the sum is 28.

The square root of 201665521 is about 14200.8985983282. The cubic root of 201665521 is about 586.4223998526.

The spelling of 201665521 in words is "two hundred one million, six hundred sixty-five thousand, five hundred twenty-one".