81505866 has 32 divisors (see below), whose sum is σ = 175952448. Its totient is φ = 25021440.

The previous prime is 81505843. The next prime is 81505867. The reversal of 81505866 is 66850518.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is not an unprimeable number, because it can be changed into a prime (81505867) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 44101 + ... + 45911.

It is an arithmetic number, because the mean of its divisors is an integer number (5498514).

Almost surely, 2^81505866 is an apocalyptic number.

81505866 is an abundant number, since it is smaller than the sum of its proper divisors (94446582).

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

81505866 is a wasteful number, since it uses less digits than its factorization.

81505866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2406.

The product of its (nonzero) digits is 57600, while the sum is 39.

The square root of 81505866 is about 9028.0599244799. The cubic root of 81505866 is about 433.5737247380.

The spelling of 81505866 in words is "eighty-one million, five hundred five thousand, eight hundred sixty-six".