1668991 has 4 divisors (see below), whose sum is σ = 1674000. Its totient is φ = 1663984.

The previous prime is 1668983. The next prime is 1669027. The reversal of 1668991 is 1998661.

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

It is a cyclic number.

It is not a de Polignac number, because 1668991 - 2³ = 1668983 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

1668991 is a strobogrammatic number because it is the same when read upside-down.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1668911) 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, 1966 + ... + 2683.

It is an arithmetic number, because the mean of its divisors is an integer number (418500).

2^1668991 is an apocalyptic number.

1668991 is a deficient number, since it is larger than the sum of its proper divisors (5009).

1668991 is an equidigital number, since it uses as much as digits as its factorization.

1668991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5008.

The product of its digits is 23328, while the sum is 40.

The square root of 1668991 is about 1291.8943455252. The cubic root of 1668991 is about 118.6182005857.

The spelling of 1668991 in words is "one million, six hundred sixty-eight thousand, nine hundred ninety-one".