81686761 has 4 divisors (see below), whose sum is σ = 87970372. Its totient is φ = 75403152.

The previous prime is 81686743. The next prime is 81686791. The reversal of 81686761 is 16768618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16768618 = 2 ⋅8384309.

It can be written as a sum of positive squares in 2 ways, for example, as 3258025 + 78428736 = 1805^2 + 8856^2 .

It is a cyclic number.

It is not a de Polignac number, because 81686761 - 2⁵ = 81686729 is a prime.

It is a super-2 number, since 2×81686761² = 13345453845342242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81686701) 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, 3141786 + ... + 3141811.

It is an arithmetic number, because the mean of its divisors is an integer number (21992593).

Almost surely, 2^81686761 is an apocalyptic number.

It is an amenable number.

81686761 is a deficient number, since it is larger than the sum of its proper divisors (6283611).

81686761 is a wasteful number, since it uses less digits than its factorization.

81686761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6283610.

The product of its digits is 96768, while the sum is 43.

The square root of 81686761 is about 9038.0728587459. The cubic root of 81686761 is about 433.8942471349.

The spelling of 81686761 in words is "eighty-one million, six hundred eighty-six thousand, seven hundred sixty-one".