81781673 has 4 divisors (see below), whose sum is σ = 81850308. Its totient is φ = 81713040.

The previous prime is 81781639. The next prime is 81781697. The reversal of 81781673 is 37618718.

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 22306729 + 59474944 = 4723^2 + 7712^2 .

It is a cyclic number.

It is not a de Polignac number, because 81781673 - 2¹⁶ = 81716137 is a prime.

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 81781673.

It is not an unprimeable number, because it can be changed into a prime (81781633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32498 + ... + 34923.

It is an arithmetic number, because the mean of its divisors is an integer number (20462577).

Almost surely, 2^81781673 is an apocalyptic number.

It is an amenable number.

81781673 is a deficient number, since it is larger than the sum of its proper divisors (68635).

81781673 is a wasteful number, since it uses less digits than its factorization.

81781673 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68634.

The product of its digits is 56448, while the sum is 41.

The square root of 81781673 is about 9043.3220112965. The cubic root of 81781673 is about 434.0622296038.

The spelling of 81781673 in words is "eighty-one million, seven hundred eighty-one thousand, six hundred seventy-three".