81505680 has 80 divisors (see below), whose sum is σ = 253942080. Its totient is φ = 21625344.

The previous prime is 81505607. The next prime is 81505717. The reversal of 81505680 is 8650518.

It is a tau number, because it is divible by the number of its divisors (80).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 54219 + ... + 55701.

It is an arithmetic number, because the mean of its divisors is an integer number (3174276).

Almost surely, 2^81505680 is an apocalyptic number.

81505680 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 81505680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (126971040).

81505680 is an abundant number, since it is smaller than the sum of its proper divisors (172436400).

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

81505680 is a wasteful number, since it uses less digits than its factorization.

81505680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1728 (or 1722 counting only the distinct ones).

The product of its (nonzero) digits is 9600, while the sum is 33.

The square root of 81505680 is about 9028.0496232575. The cubic root of 81505680 is about 433.5733949263.

The spelling of 81505680 in words is "eighty-one million, five hundred five thousand, six hundred eighty".