81661865 has 8 divisors (see below), whose sum is σ = 98910720. Its totient is φ = 64718512.

The previous prime is 81661837. The next prime is 81661901. The reversal of 81661865 is 56816618.

It is a happy number.

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 81661865 - 2⁸ = 81661609 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, 75785 + ... + 76854.

It is an arithmetic number, because the mean of its divisors is an integer number (12363840).

Almost surely, 2^81661865 is an apocalyptic number.

It is an amenable number.

81661865 is a deficient number, since it is larger than the sum of its proper divisors (17248855).

81661865 is a wasteful number, since it uses less digits than its factorization.

81661865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 152751.

The product of its digits is 69120, while the sum is 41.

The square root of 81661865 is about 9036.6954690307. The cubic root of 81661865 is about 433.8501627625.

The spelling of 81661865 in words is "eighty-one million, six hundred sixty-one thousand, eight hundred sixty-five".