6665991 has 4 divisors (see below), whose sum is σ = 8887992. Its totient is φ = 4443992.

The previous prime is 6665987. The next prime is 6666001. The reversal of 6665991 is 1995666.

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 6665991 - 2² = 6665987 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6665951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1110996 + ... + 1111001.

It is an arithmetic number, because the mean of its divisors is an integer number (2221998).

Almost surely, 2^6665991 is an apocalyptic number.

6665991 is a deficient number, since it is larger than the sum of its proper divisors (2222001).

6665991 is a wasteful number, since it uses less digits than its factorization.

6665991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2222000.

The product of its digits is 87480, while the sum is 42.

The square root of 6665991 is about 2581.8580518688. The cubic root of 6665991 is about 188.2008472946.

The spelling of 6665991 in words is "six million, six hundred sixty-five thousand, nine hundred ninety-one".