81565120 has 112 divisors (see below), whose sum is σ = 239133888. Its totient is φ = 25804800.

The previous prime is 81565117. The next prime is 81565129. The reversal of 81565120 is 2156518.

It is a tau number, because it is divible by the number of its divisors (112).

It is a super-2 number, since 2×81565120² = 13305737601228800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81565129) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27720 + ... + 30520.

It is an arithmetic number, because the mean of its divisors is an integer number (2135124).

Almost surely, 2^81565120 is an apocalyptic number.

81565120 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 81565120, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (119566944).

81565120 is an abundant number, since it is smaller than the sum of its proper divisors (157568768).

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

81565120 is a wasteful number, since it uses less digits than its factorization.

81565120 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2838 (or 2828 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 81565120 is about 9031.3409857008. The cubic root of 81565120 is about 433.6787672974.

The spelling of 81565120 in words is "eighty-one million, five hundred sixty-five thousand, one hundred twenty".