81017920 has 112 divisors (see below), whose sum is σ = 208867248. Its totient is φ = 29818880.

The previous prime is 81017917. The next prime is 81017921. The reversal of 81017920 is 2971018.

It can be written as a sum of positive squares in 8 ways, for example, as 6230016 + 74787904 = 2496^2 + 8648^2 .

It is a super-2 number, since 2×81017920² = 13127806722252800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81017921) 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, 288180 + ... + 288460.

Almost surely, 2^81017920 is an apocalyptic number.

81017920 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 81017920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (104433624).

81017920 is an abundant number, since it is smaller than the sum of its proper divisors (127849328).

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

81017920 is a wasteful number, since it uses less digits than its factorization.

81017920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 368 (or 358 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 28.

The square root of 81017920 is about 9000.9955004988. The cubic root of 81017920 is about 432.7067762855.

Adding to 81017920 its reverse (2971018), we get a palindrome (83988938).

The spelling of 81017920 in words is "eighty-one million, seventeen thousand, nine hundred twenty".