1665999 has 12 divisors (see below), whose sum is σ = 2471976. Its totient is φ = 1080432.

The previous prime is 1665997. The next prime is 1666003. The reversal of 1665999 is 9995661.

It is not a de Polignac number, because 1665999 - 2¹ = 1665997 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1665997) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2169 + ... + 2834.

It is an arithmetic number, because the mean of its divisors is an integer number (205998).

2^1665999 is an apocalyptic number.

1665999 is a deficient number, since it is larger than the sum of its proper divisors (805977).

1665999 is a wasteful number, since it uses less digits than its factorization.

1665999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5046 (or 5043 counting only the distinct ones).

The product of its digits is 131220, while the sum is 45.

The square root of 1665999 is about 1290.7358366451. The cubic root of 1665999 is about 118.5472759078.

The spelling of 1665999 in words is "one million, six hundred sixty-five thousand, nine hundred ninety-nine".