81851765 has 4 divisors (see below), whose sum is σ = 98222124. Its totient is φ = 65481408.

The previous prime is 81851743. The next prime is 81851789. The reversal of 81851765 is 56715818.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 56715818 = 2 ⋅28357909.

It can be written as a sum of positive squares in 2 ways, for example, as 44970436 + 36881329 = 6706^2 + 6073^2 .

It is a cyclic number.

It is not a de Polignac number, because 81851765 - 2⁶ = 81851701 is a prime.

It is a super-2 number, since 2×81851765² = 13399422867230450, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8185172 + ... + 8185181.

It is an arithmetic number, because the mean of its divisors is an integer number (24555531).

Almost surely, 2^81851765 is an apocalyptic number.

It is an amenable number.

81851765 is a deficient number, since it is larger than the sum of its proper divisors (16370359).

81851765 is a wasteful number, since it uses less digits than its factorization.

81851765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16370358.

The product of its digits is 67200, while the sum is 41.

The square root of 81851765 is about 9047.1965271016. The cubic root of 81851765 is about 434.1862003378.

The spelling of 81851765 in words is "eighty-one million, eight hundred fifty-one thousand, seven hundred sixty-five".