7999655571221 has 4 divisors (see below), whose sum is σ = 8041104564012. Its totient is φ = 7958206578432.

The previous prime is 7999655571211. The next prime is 7999655571227. The reversal of 7999655571221 is 1221755569997.

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 3021290570596 + 4978365000625 = 1738186^2 + 2231225^2 .

It is a cyclic number.

It is not a de Polignac number, because 7999655571221 - 2⁴² = 3601609060117 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7999655571227) 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, 20724496106 + ... + 20724496491.

It is an arithmetic number, because the mean of its divisors is an integer number (2010276141003).

Almost surely, 2^{7999655571221} is an apocalyptic number.

It is an amenable number.

7999655571221 is a deficient number, since it is larger than the sum of its proper divisors (41448992791).

7999655571221 is a wasteful number, since it uses less digits than its factorization.

7999655571221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 41448992790.

The product of its digits is 107163000, while the sum is 68.

The spelling of 7999655571221 in words is "seven trillion, nine hundred ninety-nine billion, six hundred fifty-five million, five hundred seventy-one thousand, two hundred twenty-one".