665105521 has 4 divisors (see below), whose sum is σ = 665538112. Its totient is φ = 664672932.

The previous prime is 665105479. The next prime is 665105543. The reversal of 665105521 is 125501566.

665105521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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: 125501566 = 2 ⋅62750783.

It is a cyclic number.

It is not a de Polignac number, because 665105521 - 2¹¹ = 665103473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665105921) 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, 213981 + ... + 217066.

It is an arithmetic number, because the mean of its divisors is an integer number (166384528).

Almost surely, 2^665105521 is an apocalyptic number.

It is an amenable number.

665105521 is a deficient number, since it is larger than the sum of its proper divisors (432591).

665105521 is a wasteful number, since it uses less digits than its factorization.

665105521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 432590.

The product of its (nonzero) digits is 9000, while the sum is 31.

The square root of 665105521 is about 25789.6397997335. The cubic root of 665105521 is about 872.8980385970.

The spelling of 665105521 in words is "six hundred sixty-five million, one hundred five thousand, five hundred twenty-one".