665986 has 4 divisors (see below), whose sum is σ = 998982. Its totient is φ = 332992.

The previous prime is 665983. The next prime is 665993. The reversal of 665986 is 689566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 342225 + 323761 = 585^2 + 569^2 .

It is not an unprimeable number, because it can be changed into a prime (665981) 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 as a sum of consecutive naturals, namely, 166495 + ... + 166498.

2⁶⁶⁵⁹⁸⁶ is an apocalyptic number.

665986 is a deficient number, since it is larger than the sum of its proper divisors (332996).

665986 is a wasteful number, since it uses less digits than its factorization.

665986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332995.

The product of its digits is 77760, while the sum is 40.

The square root of 665986 is about 816.0796529751. The cubic root of 665986 is about 87.3283054943.

The spelling of 665986 in words is "six hundred sixty-five thousand, nine hundred eighty-six".