81720139 has 8 divisors (see below), whose sum is σ = 86840208. Its totient is φ = 76634880.

The previous prime is 81720137. The next prime is 81720157. The reversal of 81720139 is 93102718.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81720139 - 2¹ = 81720137 is a prime.

It is a super-2 number, since 2×81720139² = 13356362236358642, 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 81720139.

It is not an unprimeable number, because it can be changed into a prime (81720137) 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, 3777 + ... + 13330.

It is an arithmetic number, because the mean of its divisors is an integer number (10855026).

Almost surely, 2^81720139 is an apocalyptic number.

81720139 is a deficient number, since it is larger than the sum of its proper divisors (5120069).

81720139 is a wasteful number, since it uses less digits than its factorization.

81720139 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17405.

The product of its (nonzero) digits is 3024, while the sum is 31.

The square root of 81720139 is about 9039.9191921167. The cubic root of 81720139 is about 433.9533368817.

The spelling of 81720139 in words is "eighty-one million, seven hundred twenty thousand, one hundred thirty-nine".