81665100 has 216 divisors, whose sum is σ = 285575472. Its totient is φ = 19353600.

The previous prime is 81665083. The next prime is 81665107. The reversal of 81665100 is 156618.

81665100 is a `hidden beast` number, since 8 + 1 + 6 + 651 + 0 + 0 = 666.

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (81665107) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 722644 + ... + 722756.

Almost surely, 2^81665100 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81665100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (142787736).

81665100 is an abundant number, since it is smaller than the sum of its proper divisors (203910372).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81665100 is a wasteful number, since it uses less digits than its factorization.

81665100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217 (or 207 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 27.

The square root of 81665100 is about 9036.8744596791. The cubic root of 81665100 is about 433.8558916167.

The spelling of 81665100 in words is "eighty-one million, six hundred sixty-five thousand, one hundred".