6561617641 has 4 divisors (see below), whose sum is σ = 6561913300. Its totient is φ = 6561321984.

The previous prime is 6561617609. The next prime is 6561617659. The reversal of 6561617641 is 1467161656.

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 6432681616 + 128936025 = 80204^2 + 11355^2 .

It is a cyclic number.

It is not a de Polignac number, because 6561617641 - 2⁵ = 6561617609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6561617441) 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 in 3 ways as a sum of consecutive naturals, for example, 111576 + ... + 159913.

It is an arithmetic number, because the mean of its divisors is an integer number (1640478325).

Almost surely, 2^6561617641 is an apocalyptic number.

It is an amenable number.

6561617641 is a deficient number, since it is larger than the sum of its proper divisors (295659).

6561617641 is a wasteful number, since it uses less digits than its factorization.

6561617641 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 295658.

The product of its digits is 181440, while the sum is 43.

The square root of 6561617641 is about 81003.8125090418. The cubic root of 6561617641 is about 1872.1341835332.

The spelling of 6561617641 in words is "six billion, five hundred sixty-one million, six hundred seventeen thousand, six hundred forty-one".