6991921 has 4 divisors (see below), whose sum is σ = 6999412. Its totient is φ = 6984432.

The previous prime is 6991903. The next prime is 6991939. The reversal of 6991921 is 1291996.

It is the 1080-th star number.

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 is an interprime number because it is at equal distance from previous prime (6991903) and next prime (6991939).

It can be written as a sum of positive squares in 2 ways, for example, as 3381921 + 3610000 = 1839^2 + 1900^2 .

It is a cyclic number.

It is not a de Polignac number, because 6991921 - 2⁵ = 6991889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6991951) 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, 2106 + ... + 4291.

It is an arithmetic number, because the mean of its divisors is an integer number (1749853).

Almost surely, 2^6991921 is an apocalyptic number.

It is an amenable number.

6991921 is a deficient number, since it is larger than the sum of its proper divisors (7491).

6991921 is a wasteful number, since it uses less digits than its factorization.

6991921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7490.

The product of its digits is 8748, while the sum is 37.

The square root of 6991921 is about 2644.2240827887. The cubic root of 6991921 is about 191.2194967514.

The spelling of 6991921 in words is "six million, nine hundred ninety-one thousand, nine hundred twenty-one".