• 161 can be written using four 4's:

• 161 is the least > 0 such that

161 has 4 divisors (see below), whose sum is σ = 192. Its totient is φ = 132.

The previous prime is 157. The next prime is 163.

161 = T_{3} + T_{4} + ... +
T_{9}.

161 is nontrivially palindromic in base 10.

161 is an esthetic number in base 15, because in such base its adjacent digits differ by 1.

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 a Cullen number, since it is equal to 5×2^{5}+1.

It is not a de Polignac number, because 161 - 2^{2} = 157 is a prime.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

161 is an undulating number in base 10.

It is a plaindrome in base 3, base 9, base 11, base 12 and base 15.

It is a nialpdrome in base 7, base 13, base 14 and 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 161.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5 + ... + 18.

It is an arithmetic number, because the mean of its divisors is an integer number (48).

It is a Proth number, since it is equal to 5 ⋅ 2^{5} + 1 and 5 < 2^{5}.

It is an amenable number.

161 is a deficient number, since it is larger than the sum of its proper divisors (31).

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

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

The sum of its prime factors is 30.

The product of its digits is 6, while the sum is 8.

The square root of 161 is about 12.6885775404. The cubic root of 161 is about 5.4401218254.

The spelling of 161 in words is "one hundred sixty-one", and thus it is an aban number.

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