6665561561 has 8 divisors (see below), whose sum is σ = 6777498504. Its totient is φ = 6553710720.

The previous prime is 6665561557. The next prime is 6665561597. The reversal of 6665561561 is 1651655666.

It can be written as a sum of positive squares in 4 ways, for example, as 2691015625 + 3974545936 = 51875^2 + 63044^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 6665561561 - 2² = 6665561557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6665566561) 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 7 ways as a sum of consecutive naturals, for example, 145355 + ... + 185631.

It is an arithmetic number, because the mean of its divisors is an integer number (847187313).

Almost surely, 2^6665561561 is an apocalyptic number.

6665561561 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

6665561561 is a deficient number, since it is larger than the sum of its proper divisors (111936943).

6665561561 is a wasteful number, since it uses less digits than its factorization.

6665561561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43051.

The product of its digits is 972000, while the sum is 47.

The square root of 6665561561 is about 81642.8904498120. The cubic root of 6665561561 is about 1881.9680575905.

The spelling of 6665561561 in words is "six billion, six hundred sixty-five million, five hundred sixty-one thousand, five hundred sixty-one".