161661 has 4 divisors (see below), whose sum is σ = 215552. Its totient is φ = 107772.

The previous prime is 161659. The next prime is 161683. The reversal of 161661 is 166161.

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 not a de Polignac number, because 161661 - 2¹ = 161659 is a prime.

It is a super-2 number, since 2×161661² = 52268557842, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a plaindrome in base 16.

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 161661.

It is not an unprimeable number, because it can be changed into a prime (161611) 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, 26941 + ... + 26946.

It is an arithmetic number, because the mean of its divisors is an integer number (53888).

2¹⁶¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

161661 is a deficient number, since it is larger than the sum of its proper divisors (53891).

161661 is an equidigital number, since it uses as much as digits as its factorization.

161661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53890.

The product of its digits is 216, while the sum is 21.

The square root of 161661 is about 402.0708892720. The cubic root of 161661 is about 54.4755662996.

The spelling of 161661 in words is "one hundred sixty-one thousand, six hundred sixty-one".