81720385 has 4 divisors (see below), whose sum is σ = 98064468. Its totient is φ = 65376304.

The previous prime is 81720313. The next prime is 81720409. The reversal of 81720385 is 58302718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 58302718 = 2 ⋅29151359.

It can be written as a sum of positive squares in 2 ways, for example, as 19562929 + 62157456 = 4423^2 + 7884^2 .

It is a cyclic number.

It is not a de Polignac number, because 81720385 - 2⁹ = 81719873 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 81720385.

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, 8172034 + ... + 8172043.

It is an arithmetic number, because the mean of its divisors is an integer number (24516117).

Almost surely, 2^81720385 is an apocalyptic number.

It is an amenable number.

81720385 is a deficient number, since it is larger than the sum of its proper divisors (16344083).

81720385 is a wasteful number, since it uses less digits than its factorization.

81720385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16344082.

The product of its (nonzero) digits is 13440, while the sum is 34.

The square root of 81720385 is about 9039.9327984228. The cubic root of 81720385 is about 433.9537723207.

The spelling of 81720385 in words is "eighty-one million, seven hundred twenty thousand, three hundred eighty-five".