81566720 has 88 divisors (see below), whose sum is σ = 198968400. Its totient is φ = 32079872.

The previous prime is 81566711. The next prime is 81566747. The reversal of 81566720 is 2766518.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 455591 + ... + 455769.

Almost surely, 2^81566720 is an apocalyptic number.

81566720 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 81566720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99484200).

81566720 is an abundant number, since it is smaller than the sum of its proper divisors (117401680).

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

81566720 is a wasteful number, since it uses less digits than its factorization.

81566720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 293 (or 275 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 81566720 is about 9031.4295656889. The cubic root of 81566720 is about 433.6816029927.

The spelling of 81566720 in words is "eighty-one million, five hundred sixty-six thousand, seven hundred twenty".