81666720 has 72 divisors (see below), whose sum is σ = 278692596. Its totient is φ = 21777408.

The previous prime is 81666719. The next prime is 81666757. The reversal of 81666720 is 2766618.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 81649296 + 17424 = 9036^2 + 132^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26917 + ... + 29796.

Almost surely, 2^81666720 is an apocalyptic number.

81666720 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81666720 is an abundant number, since it is smaller than the sum of its proper divisors (197025876).

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

81666720 is a wasteful number, since it uses less digits than its factorization.

81666720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56734 (or 56723 counting only the distinct ones).

The product of its (nonzero) digits is 24192, while the sum is 36.

The square root of 81666720 is about 9036.9640919946. The cubic root of 81666720 is about 433.8587604142.

The spelling of 81666720 in words is "eighty-one million, six hundred sixty-six thousand, seven hundred twenty".