81580820 has 12 divisors (see below), whose sum is σ = 171319764. Its totient is φ = 32632320.

The previous prime is 81580801. The next prime is 81580823. The reversal of 81580820 is 2808518.

It can be written as a sum of positive squares in 2 ways, for example, as 20052484 + 61528336 = 4478^2 + 7844^2 .

It is a hoax number, since the sum of its digits (32) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81580823) 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 3 ways as a sum of consecutive naturals, for example, 2039501 + ... + 2039540.

It is an arithmetic number, because the mean of its divisors is an integer number (14276647).

Almost surely, 2^81580820 is an apocalyptic number.

It is an amenable number.

81580820 is an abundant number, since it is smaller than the sum of its proper divisors (89738944).

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

81580820 is a wasteful number, since it uses less digits than its factorization.

81580820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4079050 (or 4079048 counting only the distinct ones).

The product of its (nonzero) digits is 5120, while the sum is 32.

The square root of 81580820 is about 9032.2101392738. The cubic root of 81580820 is about 433.7065909546.

The spelling of 81580820 in words is "eighty-one million, five hundred eighty thousand, eight hundred twenty".