6509991 has 4 divisors (see below), whose sum is σ = 8679992. Its totient is φ = 4339992.

The previous prime is 6509977. The next prime is 6510011. The reversal of 6509991 is 1999056.

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

It is not a de Polignac number, because 6509991 - 2⁷ = 6509863 is a prime.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6509941) 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, 1084996 + ... + 1085001.

It is an arithmetic number, because the mean of its divisors is an integer number (2169998).

Almost surely, 2^6509991 is an apocalyptic number.

6509991 is a deficient number, since it is larger than the sum of its proper divisors (2170001).

6509991 is a wasteful number, since it uses less digits than its factorization.

6509991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2170000.

The product of its (nonzero) digits is 21870, while the sum is 39.

The square root of 6509991 is about 2551.4684007450. The cubic root of 6509991 is about 186.7211281707.

The spelling of 6509991 in words is "six million, five hundred nine thousand, nine hundred ninety-one".