2161257561 has 12 divisors (see below), whose sum is σ = 3124515888. Its totient is φ = 1439592504.

The previous prime is 2161257557. The next prime is 2161257569. The reversal of 2161257561 is 1657521612.

2161257561 is a `hidden beast` number, since 2 + 16 + 12 + 575 + 61 = 666.

It is not a de Polignac number, because 2161257561 - 2² = 2161257557 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (2161257569) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 92775 + ... + 113708.

It is an arithmetic number, because the mean of its divisors is an integer number (260376324).

Almost surely, 2^2161257561 is an apocalyptic number.

It is an amenable number.

2161257561 is a deficient number, since it is larger than the sum of its proper divisors (963258327).

2161257561 is a wasteful number, since it uses less digits than its factorization.

2161257561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 207652 (or 207649 counting only the distinct ones).

The product of its digits is 25200, while the sum is 36.

The square root of 2161257561 is about 46489.3273881221. The cubic root of 2161257561 is about 1292.9116295208.

The spelling of 2161257561 in words is "two billion, one hundred sixty-one million, two hundred fifty-seven thousand, five hundred sixty-one".