6987991 has 4 divisors (see below), whose sum is σ = 7355800. Its totient is φ = 6620184.

The previous prime is 6987983. The next prime is 6988039. The reversal of 6987991 is 1997896.

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 6987991 - 2³ = 6987983 is a prime.

It is a Duffinian number.

6987991 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6987941) 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, 183876 + ... + 183913.

It is an arithmetic number, because the mean of its divisors is an integer number (1838950).

Almost surely, 2^6987991 is an apocalyptic number.

6987991 is a deficient number, since it is larger than the sum of its proper divisors (367809).

6987991 is a wasteful number, since it uses less digits than its factorization.

6987991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 367808.

The product of its digits is 244944, while the sum is 49.

The square root of 6987991 is about 2643.4808491835. The cubic root of 6987991 is about 191.1836633247.

The spelling of 6987991 in words is "six million, nine hundred eighty-seven thousand, nine hundred ninety-one".