6561237833721 has 12 divisors (see below), whose sum is σ = 9477878335380. Its totient is φ = 4373911726080.

The previous prime is 6561237833719. The next prime is 6561237833753. The reversal of 6561237833721 is 1273387321656.

6561237833721 is a `hidden beast` number, since 6 + 56 + 1 + 237 + 8 + 337 + 21 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 5312398058496 + 1248839775225 = 2304864^2 + 1117515^2 .

It is not a de Polignac number, because 6561237833721 - 2¹ = 6561237833719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (6561237833221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 20400720 + ... + 20719841.

It is an arithmetic number, because the mean of its divisors is an integer number (789823194615).

Almost surely, 2^{6561237833721} is an apocalyptic number.

It is an amenable number.

6561237833721 is a deficient number, since it is larger than the sum of its proper divisors (2916640501659).

6561237833721 is a wasteful number, since it uses less digits than its factorization.

6561237833721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41138296 (or 41138293 counting only the distinct ones).

The product of its digits is 7620480, while the sum is 54.

The spelling of 6561237833721 in words is "six trillion, five hundred sixty-one billion, two hundred thirty-seven million, eight hundred thirty-three thousand, seven hundred twenty-one".