2161356556561 has 4 divisors (see below), whose sum is σ = 2193615609712. Its totient is φ = 2129097503412.

The previous prime is 2161356556537. The next prime is 2161356556607. The reversal of 2161356556561 is 1656556531612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 2161356556561 - 2⁵ = 2161356556529 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 2161356556499 and 2161356556508.

It is not an unprimeable number, because it can be changed into a prime (2161356556061) 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 3 ways as a sum of consecutive naturals, for example, 16129526475 + ... + 16129526608.

It is an arithmetic number, because the mean of its divisors is an integer number (548403902428).

Almost surely, 2^{2161356556561} is an apocalyptic number.

It is an amenable number.

2161356556561 is a deficient number, since it is larger than the sum of its proper divisors (32259053151).

2161356556561 is an equidigital number, since it uses as much as digits as its factorization.

2161356556561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32259053150.

The product of its digits is 4860000, while the sum is 52.

The spelling of 2161356556561 in words is "two trillion, one hundred sixty-one billion, three hundred fifty-six million, five hundred fifty-six thousand, five hundred sixty-one".