81605520 has 60 divisors (see below), whose sum is σ = 274060956. Its totient is φ = 21761280.

The previous prime is 81605497. The next prime is 81605521. The reversal of 81605520 is 2550618.

81605520 is a `hidden beast` number, since 8 + 1 + 605 + 52 + 0 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 24088464 + 57517056 = 4908^2 + 7584^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is not an unprimeable number, because it can be changed into a prime (81605521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 55951 + ... + 57390.

Almost surely, 2^81605520 is an apocalyptic number.

81605520 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81605520 is an abundant number, since it is smaller than the sum of its proper divisors (192455436).

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

81605520 is a wasteful number, since it uses less digits than its factorization.

81605520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 113360 (or 113351 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 27.

The square root of 81605520 is about 9033.5773644775. The cubic root of 81605520 is about 433.7503572543.

The spelling of 81605520 in words is "eighty-one million, six hundred five thousand, five hundred twenty".