161911681 has 4 divisors (see below), whose sum is σ = 161944000. Its totient is φ = 161879364.

The previous prime is 161911657. The next prime is 161911699. The reversal of 161911681 is 186119161.

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, and also an emirpimes, since its reverse is a distinct semiprime: 186119161 = 431 ⋅431831.

It is a cyclic number.

It is not a de Polignac number, because 161911681 - 2¹⁷ = 161780609 is a prime.

It is a super-2 number, since 2×161911681² = 52430784888491522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (161911601) 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, 6861 + ... + 19258.

It is an arithmetic number, because the mean of its divisors is an integer number (40486000).

Almost surely, 2^161911681 is an apocalyptic number.

It is an amenable number.

161911681 is a deficient number, since it is larger than the sum of its proper divisors (32319).

161911681 is an equidigital number, since it uses as much as digits as its factorization.

161911681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32318.

The product of its digits is 2592, while the sum is 34.

The square root of 161911681 is about 12724.4520903652. The cubic root of 161911681 is about 545.0370942403.

The spelling of 161911681 in words is "one hundred sixty-one million, nine hundred eleven thousand, six hundred eighty-one".