81841681 has 4 divisors (see below), whose sum is σ = 81989172. Its totient is φ = 81694192.

The previous prime is 81841663. The next prime is 81841703. The reversal of 81841681 is 18614818.

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 23853456 + 57988225 = 4884^2 + 7615^2 .

It is a cyclic number.

It is not a de Polignac number, because 81841681 - 2¹¹ = 81839633 is a prime.

It is a super-2 number, since 2×81841681² = 13396121497811522, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81841681.

It is not an unprimeable number, because it can be changed into a prime (81841651) by changing a digit.

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, 72910 + ... + 74023.

It is an arithmetic number, because the mean of its divisors is an integer number (20497293).

Almost surely, 2^81841681 is an apocalyptic number.

It is an amenable number.

81841681 is a deficient number, since it is larger than the sum of its proper divisors (147491).

81841681 is a wasteful number, since it uses less digits than its factorization.

81841681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147490.

The product of its digits is 12288, while the sum is 37.

The square root of 81841681 is about 9046.6392102261. The cubic root of 81841681 is about 434.1683692686.

The spelling of 81841681 in words is "eighty-one million, eight hundred forty-one thousand, six hundred eighty-one".