81666544 has 20 divisors (see below), whose sum is σ = 158499280. Its totient is φ = 40763520.

The previous prime is 81666509. The next prime is 81666551. The reversal of 81666544 is 44566618.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 81666497 and 81666506.

It is a congruent number.

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 3 ways as a sum of consecutive naturals, for example, 6052 + ... + 14140.

It is an arithmetic number, because the mean of its divisors is an integer number (7924964).

Almost surely, 2^81666544 is an apocalyptic number.

It is an amenable number.

81666544 is a deficient number, since it is larger than the sum of its proper divisors (76832736).

81666544 is a wasteful number, since it uses less digits than its factorization.

81666544 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8728 (or 8722 counting only the distinct ones).

The product of its digits is 138240, while the sum is 40.

The square root of 81666544 is about 9036.9543542058. The cubic root of 81666544 is about 433.8584487442.

The spelling of 81666544 in words is "eighty-one million, six hundred sixty-six thousand, five hundred forty-four".