2161616660561 has 4 divisors (see below), whose sum is σ = 2161643297124. Its totient is φ = 2161590024000.

The previous prime is 2161616660549. The next prime is 2161616660641. The reversal of 2161616660561 is 1650666161612.

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 1167296572225 + 994320088336 = 1080415^2 + 997156^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-2161616660561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2161616660501) 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, 13196180 + ... + 13358981.

It is an arithmetic number, because the mean of its divisors is an integer number (540410824281).

Almost surely, 2^{2161616660561} is an apocalyptic number.

It is an amenable number.

2161616660561 is a deficient number, since it is larger than the sum of its proper divisors (26636563).

2161616660561 is an equidigital number, since it uses as much as digits as its factorization.

2161616660561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26636562.

The product of its (nonzero) digits is 466560, while the sum is 47.

The spelling of 2161616660561 in words is "two trillion, one hundred sixty-one billion, six hundred sixteen million, six hundred sixty thousand, five hundred sixty-one".