81720478 has 16 divisors (see below), whose sum is σ = 140516064. Its totient is φ = 34917120.

The previous prime is 81720473. The next prime is 81720491. The reversal of 81720478 is 87402718.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81720473) 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 7 ways as a sum of consecutive naturals, for example, 3943 + ... + 13378.

It is an arithmetic number, because the mean of its divisors is an integer number (8782254).

Almost surely, 2^81720478 is an apocalyptic number.

81720478 is a deficient number, since it is larger than the sum of its proper divisors (58795586).

81720478 is a wasteful number, since it uses less digits than its factorization.

81720478 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17667.

The product of its (nonzero) digits is 25088, while the sum is 37.

The square root of 81720478 is about 9039.9379422649. The cubic root of 81720478 is about 433.9539369377.

The spelling of 81720478 in words is "eighty-one million, seven hundred twenty thousand, four hundred seventy-eight".