81133520 has 120 divisors (see below), whose sum is σ = 216890136. Its totient is φ = 28114944.

The previous prime is 81133517. The next prime is 81133523. The reversal of 81133520 is 2533118.

It is an interprime number because it is at equal distance from previous prime (81133517) and next prime (81133523).

It can be written as a sum of positive squares in 12 ways, for example, as 37994896 + 43138624 = 6164^2 + 6568^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81133523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 229664 + ... + 230016.

Almost surely, 2^81133520 is an apocalyptic number.

81133520 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 81133520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (108445068).

81133520 is an abundant number, since it is smaller than the sum of its proper divisors (135756616).

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

81133520 is a wasteful number, since it uses less digits than its factorization.

81133520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 409 (or 390 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 81133520 is about 9007.4147234376. The cubic root of 81133520 is about 432.9124802890.

Adding to 81133520 its reverse (2533118), we get a palindrome (83666638).

The spelling of 81133520 in words is "eighty-one million, one hundred thirty-three thousand, five hundred twenty".