2161757981 has 4 divisors (see below), whose sum is σ = 2162004864. Its totient is φ = 2161511100.

The previous prime is 2161757977. The next prime is 2161757993. The reversal of 2161757981 is 1897571612.

2161757981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 2161757981 - 2² = 2161757977 is a prime.

It is a super-2 number, since 2×2161757981² = 9346395136834392722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2161757911) 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, 109805 + ... + 127986.

It is an arithmetic number, because the mean of its divisors is an integer number (540501216).

Almost surely, 2^2161757981 is an apocalyptic number.

It is an amenable number.

2161757981 is a deficient number, since it is larger than the sum of its proper divisors (246883).

2161757981 is an equidigital number, since it uses as much as digits as its factorization.

2161757981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 246882.

The product of its digits is 211680, while the sum is 47.

The square root of 2161757981 is about 46494.7091721198. The cubic root of 2161757981 is about 1293.0114092232.

The spelling of 2161757981 in words is "two billion, one hundred sixty-one million, seven hundred fifty-seven thousand, nine hundred eighty-one".