665665521 has 4 divisors (see below), whose sum is σ = 887554032. Its totient is φ = 443777012.

The previous prime is 665665493. The next prime is 665665523. The reversal of 665665521 is 125566566.

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.

It is a cyclic number.

It is not a de Polignac number, because 665665521 - 2⁶ = 665665457 is a prime.

It is a super-2 number, since 2×665665521² = 886221171696402882, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (665665523) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 110944251 + ... + 110944256.

It is an arithmetic number, because the mean of its divisors is an integer number (221888508).

Almost surely, 2^665665521 is an apocalyptic number.

It is an amenable number.

665665521 is a deficient number, since it is larger than the sum of its proper divisors (221888511).

665665521 is a wasteful number, since it uses less digits than its factorization.

665665521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221888510.

The product of its digits is 324000, while the sum is 42.

The square root of 665665521 is about 25800.4945882826. The cubic root of 665665521 is about 873.1429550093.

The spelling of 665665521 in words is "six hundred sixty-five million, six hundred sixty-five thousand, five hundred twenty-one".