6991999889121 has 27 divisors (see below), whose sum is σ = 10936366255737. Its totient is φ = 4302705700800.

The previous prime is 6991999889093. The next prime is 6991999889177. The reversal of 6991999889121 is 1219889991996.

The square root of 6991999889121 is 2644239.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 1069766147025 + 5922233742096 = 1034295^2 + 2433564^2 .

It is not a de Polignac number, because 6991999889121 - 2¹¹ = 6991999887073 is a prime.

It is a super-3 number, since 3×6991999889121³ (a number of 40 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (6991999889621) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 103091421 + ... + 103159221.

Almost surely, 2^{6991999889121} is an apocalyptic number.

6991999889121 is the 2644239-th square number.

6991999889121 is the 1322120-th centered octagonal number.

It is an amenable number.

6991999889121 is a deficient number, since it is larger than the sum of its proper divisors (3944366366616).

6991999889121 is an frugal number, since it uses more digits than its factorization.

6991999889121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 135634 (or 67817 counting only the distinct ones).

The product of its digits is 408146688, while the sum is 81.

Multiplying 6991999889121 by its sum of digits (81), we get a square (566351991018801 = 23798151²).

The spelling of 6991999889121 in words is "six trillion, nine hundred ninety-one billion, nine hundred ninety-nine million, eight hundred eighty-nine thousand, one hundred twenty-one".