81807785 has 4 divisors (see below), whose sum is σ = 98169348. Its totient is φ = 65446224.

The previous prime is 81807767. The next prime is 81807793. The reversal of 81807785 is 58770818.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 58690921 + 23116864 = 7661^2 + 4808^2 .

It is a cyclic number.

It is not a de Polignac number, because 81807785 - 2¹⁴ = 81791401 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8180774 + ... + 8180783.

It is an arithmetic number, because the mean of its divisors is an integer number (24542337).

Almost surely, 2^81807785 is an apocalyptic number.

It is an amenable number.

81807785 is a deficient number, since it is larger than the sum of its proper divisors (16361563).

81807785 is a wasteful number, since it uses less digits than its factorization.

81807785 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16361562.

The product of its (nonzero) digits is 125440, while the sum is 44.

The square root of 81807785 is about 9044.7656133258. The cubic root of 81807785 is about 434.1084218065.

The spelling of 81807785 in words is "eighty-one million, eight hundred seven thousand, seven hundred eighty-five".