161681666 has 4 divisors (see below), whose sum is σ = 242522502. Its totient is φ = 80840832.

The previous prime is 161681633. The next prime is 161681669. The reversal of 161681666 is 666186161.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 666186161 = 463 ⋅1438847.

It can be written as a sum of positive squares in only one way, i.e., 156775441 + 4906225 = 12521^2 + 2215^2 .

It is a super-2 number, since 2×161681666² = 52281922241071112, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161681669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40420415 + ... + 40420418.

Almost surely, 2^161681666 is an apocalyptic number.

161681666 is a deficient number, since it is larger than the sum of its proper divisors (80840836).

161681666 is an equidigital number, since it uses as much as digits as its factorization.

161681666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80840835.

The product of its digits is 62208, while the sum is 41.

The square root of 161681666 is about 12715.4105714287. The cubic root of 161681666 is about 544.7788750278.

The spelling of 161681666 in words is "one hundred sixty-one million, six hundred eighty-one thousand, six hundred sixty-six".