161311781 has 8 divisors (see below), whose sum is σ = 162379800. Its totient is φ = 160247808.

The previous prime is 161311769. The next prime is 161311783. The reversal of 161311781 is 187113161.

161311781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 56761156 + 104550625 = 7534^2 + 10225^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 161311781 - 2¹⁴ = 161295397 is a prime.

It is a super-2 number, since 2×161311781² = 52042981378783922, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161311783) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 123725 + ... + 125021.

It is an arithmetic number, because the mean of its divisors is an integer number (20297475).

Almost surely, 2^161311781 is an apocalyptic number.

It is an amenable number.

161311781 is a deficient number, since it is larger than the sum of its proper divisors (1068019).

161311781 is a wasteful number, since it uses less digits than its factorization.

161311781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2023.

The product of its digits is 1008, while the sum is 29.

The square root of 161311781 is about 12700.8574907366. The cubic root of 161311781 is about 544.3631210371.

The spelling of 161311781 in words is "one hundred sixty-one million, three hundred eleven thousand, seven hundred eighty-one".