81655840 has 48 divisors (see below), whose sum is σ = 220473792. Its totient is φ = 27995904.

The previous prime is 81655813. The next prime is 81655841. The reversal of 81655840 is 4855618.

It is a super-3 number, since 3×81655840³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a self number, because there is not a number n which added to its sum of digits gives 81655840.

It is not an unprimeable number, because it can be changed into a prime (81655841) 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 7 ways as a sum of consecutive naturals, for example, 35334 + ... + 37573.

It is an arithmetic number, because the mean of its divisors is an integer number (4593204).

Almost surely, 2^81655840 is an apocalyptic number.

81655840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81655840 is an abundant number, since it is smaller than the sum of its proper divisors (138817952).

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

81655840 is a wasteful number, since it uses less digits than its factorization.

81655840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72929 (or 72921 counting only the distinct ones).

The product of its (nonzero) digits is 38400, while the sum is 37.

The square root of 81655840 is about 9036.3620998718. The cubic root of 81655840 is about 433.8394927004.

The spelling of 81655840 in words is "eighty-one million, six hundred fifty-five thousand, eight hundred forty".