665261 has 4 divisors (see below), whose sum is σ = 704412. Its totient is φ = 626112.

The previous prime is 665251. The next prime is 665267. The reversal of 665261 is 162566.

665261 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 an emirpimes, since its reverse is a distinct semiprime: 162566 = 2 ⋅81283.

It can be written as a sum of positive squares in 2 ways, for example, as 592900 + 72361 = 770^2 + 269^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665261 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 665261.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665267) 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, 19550 + ... + 19583.

It is an arithmetic number, because the mean of its divisors is an integer number (176103).

2⁶⁶⁵²⁶¹ is an apocalyptic number.

It is an amenable number.

665261 is a deficient number, since it is larger than the sum of its proper divisors (39151).

665261 is a wasteful number, since it uses less digits than its factorization.

665261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39150.

The product of its digits is 2160, while the sum is 26.

The square root of 665261 is about 815.6353351836. The cubic root of 665261 is about 87.2966051233.

The spelling of 665261 in words is "six hundred sixty-five thousand, two hundred sixty-one".