81666717 has 8 divisors (see below), whose sum is σ = 118788000. Its totient is φ = 49494960.

The previous prime is 81666713. The next prime is 81666719. The reversal of 81666717 is 71766618.

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

It is not a de Polignac number, because 81666717 - 2² = 81666713 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81666713) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1237342 + ... + 1237407.

It is an arithmetic number, because the mean of its divisors is an integer number (14848500).

Almost surely, 2^81666717 is an apocalyptic number.

It is an amenable number.

81666717 is a deficient number, since it is larger than the sum of its proper divisors (37121283).

81666717 is a wasteful number, since it uses less digits than its factorization.

81666717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2474763.

The product of its digits is 84672, while the sum is 42.

The square root of 81666717 is about 9036.9639260097. The cubic root of 81666717 is about 433.8587551016.

Subtracting from 81666717 its reverse (71766618), we obtain a palindrome (9900099).

The spelling of 81666717 in words is "eighty-one million, six hundred sixty-six thousand, seven hundred seventeen".