161781 has 4 divisors (see below), whose sum is σ = 215712. Its totient is φ = 107852.

The previous prime is 161779. The next prime is 161783. The reversal of 161781 is 187161.

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 an interprime number because it is at equal distance from previous prime (161779) and next prime (161783).

It is a cyclic number.

It is not a de Polignac number, because 161781 - 2¹ = 161779 is a prime.

It is a super-2 number, since 2×161781² = 52346183922, which contains 22 as substring.

It is a D-number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 161781.

It is not an unprimeable number, because it can be changed into a prime (161783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26961 + ... + 26966.

It is an arithmetic number, because the mean of its divisors is an integer number (53928).

2¹⁶¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

161781 is a deficient number, since it is larger than the sum of its proper divisors (53931).

161781 is an equidigital number, since it uses as much as digits as its factorization.

161781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53930.

The product of its digits is 336, while the sum is 24.

The square root of 161781 is about 402.2200890060. The cubic root of 161781 is about 54.4890419289.

The spelling of 161781 in words is "one hundred sixty-one thousand, seven hundred eighty-one".