81661705 has 4 divisors (see below), whose sum is σ = 97994052. Its totient is φ = 65329360.

The previous prime is 81661703. The next prime is 81661721. The reversal of 81661705 is 50716618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 50716618 = 2 ⋅25358309.

It can be written as a sum of positive squares in 2 ways, for example, as 31945104 + 49716601 = 5652^2 + 7051^2 .

It is not a de Polignac number, because 81661705 - 2¹ = 81661703 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81661703) 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, 8166166 + ... + 8166175.

It is an arithmetic number, because the mean of its divisors is an integer number (24498513).

Almost surely, 2^81661705 is an apocalyptic number.

It is an amenable number.

81661705 is a deficient number, since it is larger than the sum of its proper divisors (16332347).

81661705 is a wasteful number, since it uses less digits than its factorization.

81661705 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16332346.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 81661705 is about 9036.6866162327. The cubic root of 81661705 is about 433.8498794150.

The spelling of 81661705 in words is "eighty-one million, six hundred sixty-one thousand, seven hundred five".