1664991 has 6 divisors (see below), whose sum is σ = 2405000. Its totient is φ = 1109988.

The previous prime is 1664987. The next prime is 1665007. The reversal of 1664991 is 1994661.

1664991 is a `hidden beast` number, since 1 + 6 + 649 + 9 + 1 = 666.

It is not a de Polignac number, because 1664991 - 2² = 1664987 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1664941) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 92491 + ... + 92508.

2^1664991 is an apocalyptic number.

1664991 is a deficient number, since it is larger than the sum of its proper divisors (740009).

1664991 is a wasteful number, since it uses less digits than its factorization.

1664991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 185005 (or 185002 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 1664991 is about 1290.3453026225. The cubic root of 1664991 is about 118.5233623756.

The spelling of 1664991 in words is "one million, six hundred sixty-four thousand, nine hundred ninety-one".