81681680 has 40 divisors (see below), whose sum is σ = 190992984. Its totient is φ = 32486400.

The previous prime is 81681679. The next prime is 81681689. The reversal of 81681680 is 8618618.

It can be written as a sum of positive squares in 4 ways, for example, as 8133904 + 73547776 = 2852^2 + 8576^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (81681689) 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 7 ways as a sum of consecutive naturals, for example, 11660 + ... + 17300.

Almost surely, 2^81681680 is an apocalyptic number.

81681680 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 81681680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (95496492).

81681680 is an abundant number, since it is smaller than the sum of its proper divisors (109311304).

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

81681680 is a wasteful number, since it uses less digits than its factorization.

81681680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5835 (or 5829 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 38.

The square root of 81681680 is about 9037.7917656914. The cubic root of 81681680 is about 433.8852507266.

The spelling of 81681680 in words is "eighty-one million, six hundred eighty-one thousand, six hundred eighty".