81666640 has 160 divisors (see below), whose sum is σ = 225628416. Its totient is φ = 27156480.

The previous prime is 81666631. The next prime is 81666647. The reversal of 81666640 is 4666618.

It is a self number, because there is not a number n which added to its sum of digits gives 81666640.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81666647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 792829 + ... + 792931.

Almost surely, 2^81666640 is an apocalyptic number.

81666640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81666640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (112814208).

81666640 is an abundant number, since it is smaller than the sum of its proper divisors (143961776).

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

81666640 is a wasteful number, since it uses less digits than its factorization.

81666640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 197 (or 191 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 37.

The square root of 81666640 is about 9036.9596657283. The cubic root of 81666640 is about 433.8586187460.

The spelling of 81666640 in words is "eighty-one million, six hundred sixty-six thousand, six hundred forty".