81720693 has 6 divisors (see below), whose sum is σ = 118041014. Its totient is φ = 54480456.

The previous prime is 81720673. The next prime is 81720697. The reversal of 81720693 is 39602718.

It can be written as a sum of positive squares in only one way, i.e., 76160529 + 5560164 = 8727^2 + 2358^2 .

It is not a de Polignac number, because 81720693 - 2⁸ = 81720437 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81720697) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4540030 + ... + 4540047.

Almost surely, 2^81720693 is an apocalyptic number.

It is an amenable number.

81720693 is a deficient number, since it is larger than the sum of its proper divisors (36320321).

81720693 is a wasteful number, since it uses less digits than its factorization.

81720693 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9080083 (or 9080080 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 81720693 is about 9039.9498339316. The cubic root of 81720693 is about 433.9543175033.

The spelling of 81720693 in words is "eighty-one million, seven hundred twenty thousand, six hundred ninety-three".