81656665 has 8 divisors (see below), whose sum is σ = 98481600. Its totient is φ = 64996272.

The previous prime is 81656657. The next prime is 81656671. The reversal of 81656665 is 56665618.

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 81656665 - 2³ = 81656657 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 40039 + ... + 42028.

It is an arithmetic number, because the mean of its divisors is an integer number (12310200).

Almost surely, 2^81656665 is an apocalyptic number.

It is an amenable number.

81656665 is a deficient number, since it is larger than the sum of its proper divisors (16824935).

81656665 is a wasteful number, since it uses less digits than its factorization.

81656665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82271.

The product of its digits is 259200, while the sum is 43.

The square root of 81656665 is about 9036.4077486576. The cubic root of 81656665 is about 433.8409537773.

The spelling of 81656665 in words is "eighty-one million, six hundred fifty-six thousand, six hundred sixty-five".