161681 has 4 divisors (see below), whose sum is σ = 174132. Its totient is φ = 149232.

The previous prime is 161659. The next prime is 161683. The reversal of 161681 is 186161.

161681 = 66² + 67² + ... + 91².

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13456 + 148225 = 116^2 + 385^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161681 is a prime.

It is a super-2 number, since 2×161681² = 52281491522, which contains 22 as substring.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 161681.

It is not an unprimeable number, because it can be changed into a prime (161683) 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, 6206 + ... + 6231.

It is an arithmetic number, because the mean of its divisors is an integer number (43533).

2¹⁶¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

161681 is a deficient number, since it is larger than the sum of its proper divisors (12451).

161681 is a wasteful number, since it uses less digits than its factorization.

161681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12450.

The product of its digits is 288, while the sum is 23.

The square root of 161681 is about 402.0957597389. The cubic root of 161681 is about 54.4778127008.

It can be divided in two parts, 16 and 1681, that multiplied together give a square (26896 = 164²).

The spelling of 161681 in words is "one hundred sixty-one thousand, six hundred eighty-one".