6687991 has 4 divisors (see below), whose sum is σ = 6715984. Its totient is φ = 6660000.

The previous prime is 6687983. The next prime is 6688001. The reversal of 6687991 is 1997866.

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 6687991 - 2³ = 6687983 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 (6687931) 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, 13635 + ... + 14116.

It is an arithmetic number, because the mean of its divisors is an integer number (1678996).

Almost surely, 2^6687991 is an apocalyptic number.

6687991 is a deficient number, since it is larger than the sum of its proper divisors (27993).

6687991 is a wasteful number, since it uses less digits than its factorization.

6687991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27992.

The product of its digits is 163296, while the sum is 46.

The square root of 6687991 is about 2586.1150399779. The cubic root of 6687991 is about 188.4076618579.

The spelling of 6687991 in words is "six million, six hundred eighty-seven thousand, nine hundred ninety-one".