81331665 has 16 divisors (see below), whose sum is σ = 130531776. Its totient is φ = 43243200.

The previous prime is 81331651. The next prime is 81331669. The reversal of 81331665 is 56613318.

It is not a de Polignac number, because 81331665 - 2⁵ = 81331633 is a prime.

It is a super-2 number, since 2×81331665² = 13229679463344450, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81331669) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3226 + ... + 13155.

It is an arithmetic number, because the mean of its divisors is an integer number (8158236).

Almost surely, 2^81331665 is an apocalyptic number.

It is an amenable number.

81331665 is a deficient number, since it is larger than the sum of its proper divisors (49200111).

81331665 is a wasteful number, since it uses less digits than its factorization.

81331665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16720.

The product of its digits is 12960, while the sum is 33.

The square root of 81331665 is about 9018.4070101099. The cubic root of 81331665 is about 433.2646146783.

The spelling of 81331665 in words is "eighty-one million, three hundred thirty-one thousand, six hundred sixty-five".