2181915991161 has 9 divisors (see below), whose sum is σ = 3151662832591. Its totient is φ = 1454607706512.

The previous prime is 2181915991081. The next prime is 2181915991163. The reversal of 2181915991161 is 1611995191812.

The square root of 2181915991161 is 1477131.

It is a perfect power (a square), and thus also a powerful number.

2181915991161 is a `hidden beast` number, since 21 + 8 + 19 + 1 + 599 + 1 + 16 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 323994332025 + 1857921659136 = 569205^2 + 1363056^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 2181915991161 - 2¹⁵ = 2181915958393 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 2181915991098 and 2181915991107.

It is not an unprimeable number, because it can be changed into a prime (2181915991163) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 4185205 + ... + 4677581.

Almost surely, 2^{2181915991161} is an apocalyptic number.

2181915991161 is the 1477131-st square number.

2181915991161 is the 738566-th centered octagonal number.

It is an amenable number.

2181915991161 is a deficient number, since it is larger than the sum of its proper divisors (969746841430).

2181915991161 is an frugal number, since it uses more digits than its factorization.

2181915991161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 984760 (or 492380 counting only the distinct ones).

The product of its digits is 349920, while the sum is 54.

The spelling of 2181915991161 in words is "two trillion, one hundred eighty-one billion, nine hundred fifteen million, nine hundred ninety-one thousand, one hundred sixty-one".