6561515665 has 4 divisors (see below), whose sum is σ = 7873818804. Its totient is φ = 5249212528.

The previous prime is 6561515663. The next prime is 6561515683. The reversal of 6561515665 is 5665151656.

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 4367623744 + 2193891921 = 66088^2 + 46839^2 .

It is a cyclic number.

It is not a de Polignac number, because 6561515665 - 2¹ = 6561515663 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6561515663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 656151562 + ... + 656151571.

It is an arithmetic number, because the mean of its divisors is an integer number (1968454701).

Almost surely, 2^6561515665 is an apocalyptic number.

It is an amenable number.

6561515665 is a deficient number, since it is larger than the sum of its proper divisors (1312303139).

6561515665 is a wasteful number, since it uses less digits than its factorization.

6561515665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1312303138.

The product of its digits is 810000, while the sum is 46.

The square root of 6561515665 is about 81003.1830547417. The cubic root of 6561515665 is about 1872.1244850231.

The spelling of 6561515665 in words is "six billion, five hundred sixty-one million, five hundred fifteen thousand, six hundred sixty-five".