81205520 has 60 divisors (see below), whose sum is σ = 207551820. Its totient is φ = 29525760.

The previous prime is 81205511. The next prime is 81205547. The reversal of 81205520 is 2550218.

It can be written as a sum of positive squares in 2 ways, for example, as 51437584 + 29767936 = 7172^2 + 5456^2 .

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5486 + ... + 13874.

It is an arithmetic number, because the mean of its divisors is an integer number (3459197).

Almost surely, 2^81205520 is an apocalyptic number.

81205520 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 81205520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (103775910).

81205520 is an abundant number, since it is smaller than the sum of its proper divisors (126346300).

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

81205520 is a wasteful number, since it uses less digits than its factorization.

81205520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8424 (or 8407 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 23.

The square root of 81205520 is about 9011.4105444153. The cubic root of 81205520 is about 433.0405016989.

Adding to 81205520 its reverse (2550218), we get a palindrome (83755738).

The spelling of 81205520 in words is "eighty-one million, two hundred five thousand, five hundred twenty".