6991338721 has 2 divisors, whose sum is σ = 6991338722. Its totient is φ = 6991338720.

The previous prime is 6991338707. The next prime is 6991338733. The reversal of 6991338721 is 1278331996.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6878214225 + 113124496 = 82935^2 + 10636^2 .

It is a cyclic number.

It is not a de Polignac number, because 6991338721 - 2¹⁷ = 6991207649 is a prime.

It is a super-2 number, since 2×6991338721² = 97757634223507831682, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (6991308721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3495669360 + 3495669361.

It is an arithmetic number, because the mean of its divisors is an integer number (3495669361).

Almost surely, 2^6991338721 is an apocalyptic number.

It is an amenable number.

6991338721 is a deficient number, since it is larger than the sum of its proper divisors (1).

6991338721 is an equidigital number, since it uses as much as digits as its factorization.

6991338721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 489888, while the sum is 49.

The square root of 6991338721 is about 83614.2255899078. The cubic root of 6991338721 is about 1912.1418842535.

The spelling of 6991338721 in words is "six billion, nine hundred ninety-one million, three hundred thirty-eight thousand, seven hundred twenty-one".