6991645 has 4 divisors (see below), whose sum is σ = 8389980. Its totient is φ = 5593312.

The previous prime is 6991619. The next prime is 6991657. The reversal of 6991645 is 5461996.

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

It can be written as a sum of positive squares in 2 ways, for example, as 5212089 + 1779556 = 2283^2 + 1334^2 .

It is a cyclic number.

It is not a de Polignac number, because 6991645 - 2⁵ = 6991613 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a junction number, because it is equal to n+sod(n) for n = 6991598 and 6991607.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 699160 + ... + 699169.

It is an arithmetic number, because the mean of its divisors is an integer number (2097495).

Almost surely, 2^6991645 is an apocalyptic number.

It is an amenable number.

6991645 is a deficient number, since it is larger than the sum of its proper divisors (1398335).

6991645 is a wasteful number, since it uses less digits than its factorization.

6991645 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1398334.

The product of its digits is 58320, while the sum is 40.

The square root of 6991645 is about 2644.1718930508. The cubic root of 6991645 is about 191.2169806438.

The spelling of 6991645 in words is "six million, nine hundred ninety-one thousand, six hundred forty-five".