81555880 has 32 divisors (see below), whose sum is σ = 209715840. Its totient is φ = 27961920.

The previous prime is 81555869. The next prime is 81555893. The reversal of 81555880 is 8855518.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (40).

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 145356 + ... + 145915.

It is an arithmetic number, because the mean of its divisors is an integer number (6553620).

Almost surely, 2^81555880 is an apocalyptic number.

It is an amenable number.

81555880 is an abundant number, since it is smaller than the sum of its proper divisors (128159960).

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

81555880 is a wasteful number, since it uses less digits than its factorization.

81555880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 291289 (or 291285 counting only the distinct ones).

The product of its (nonzero) digits is 64000, while the sum is 40.

The square root of 81555880 is about 9030.8294192726. The cubic root of 81555880 is about 433.6623904313.

The spelling of 81555880 in words is "eighty-one million, five hundred fifty-five thousand, eight hundred eighty".