663999 has 12 divisors (see below), whose sum is σ = 1030104. Its totient is φ = 379344.

The previous prime is 663997. The next prime is 664009. The reversal of 663999 is 999366.

It is not a de Polignac number, because 663999 - 2¹ = 663997 is a prime.

663999 is a modest number, since divided by 999 gives 663 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 663999.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (663991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2112 + ... + 2405.

It is an arithmetic number, because the mean of its divisors is an integer number (85842).

2⁶⁶³⁹⁹⁹ is an apocalyptic number.

663999 is a deficient number, since it is larger than the sum of its proper divisors (366105).

663999 is a wasteful number, since it uses less digits than its factorization.

663999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4534 (or 4527 counting only the distinct ones).

The product of its digits is 78732, while the sum is 42.

The square root of 663999 is about 814.8613378974. The cubic root of 663999 is about 87.2413696332.

The spelling of 663999 in words is "six hundred sixty-three thousand, nine hundred ninety-nine".