6991661 has 4 divisors (see below), whose sum is σ = 6997212. Its totient is φ = 6986112.

The previous prime is 6991657. The next prime is 6991667. The reversal of 6991661 is 1661996.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 1729225 + 5262436 = 1315^2 + 2294^2 .

It is a cyclic number.

It is not a de Polignac number, because 6991661 - 2² = 6991657 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6991667) 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, 125 + ... + 3741.

It is an arithmetic number, because the mean of its divisors is an integer number (1749303).

Almost surely, 2^6991661 is an apocalyptic number.

It is an amenable number.

6991661 is a deficient number, since it is larger than the sum of its proper divisors (5551).

6991661 is a wasteful number, since it uses less digits than its factorization.

6991661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5550.

The product of its digits is 17496, while the sum is 38.

The square root of 6991661 is about 2644.1749185710. The cubic root of 6991661 is about 191.2171265069.

The spelling of 6991661 in words is "six million, nine hundred ninety-one thousand, six hundred sixty-one".