6651998991565 has 4 divisors (see below), whose sum is σ = 7982398789884. Its totient is φ = 5321599193248.

The previous prime is 6651998991509. The next prime is 6651998991601. The reversal of 6651998991565 is 5651998991566.

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 1050909969321 + 5601089022244 = 1025139^2 + 2366662^2 .

It is a cyclic number.

It is not a de Polignac number, because 6651998991565 - 2¹⁵ = 6651998958797 is a prime.

It is a super-2 number, since 2×6651998991565² (a number of 26 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 665199899152 + ... + 665199899161.

It is an arithmetic number, because the mean of its divisors is an integer number (1995599697471).

Almost surely, 2^{6651998991565} is an apocalyptic number.

It is an amenable number.

6651998991565 is a deficient number, since it is larger than the sum of its proper divisors (1330399798319).

6651998991565 is a wasteful number, since it uses less digits than its factorization.

6651998991565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1330399798318.

The product of its digits is 1417176000, while the sum is 79.

Subtracting from 6651998991565 its reverse (5651998991566), we obtain a palindrome (999999999999).

The spelling of 6651998991565 in words is "six trillion, six hundred fifty-one billion, nine hundred ninety-eight million, nine hundred ninety-one thousand, five hundred sixty-five".