665121 has 4 divisors (see below), whose sum is σ = 886832. Its totient is φ = 443412.

The previous prime is 665117. The next prime is 665123. The reversal of 665121 is 121566.

It is a happy number.

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 not a de Polignac number, because 665121 - 2² = 665117 is a prime.

It is a D-number.

It is a Duffinian number.

It is a plaindrome in base 9 and base 14.

It is not an unprimeable number, because it can be changed into a prime (665123) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 110851 + ... + 110856.

It is an arithmetic number, because the mean of its divisors is an integer number (221708).

2⁶⁶⁵¹²¹ is an apocalyptic number.

It is an amenable number.

665121 is a deficient number, since it is larger than the sum of its proper divisors (221711).

665121 is a wasteful number, since it uses less digits than its factorization.

665121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 221710.

The product of its digits is 360, while the sum is 21.

The square root of 665121 is about 815.5495080006. The cubic root of 665121 is about 87.2904810196.

Adding to 665121 its reverse (121566), we get a palindrome (786687).

The spelling of 665121 in words is "six hundred sixty-five thousand, one hundred twenty-one".