81664538 has 8 divisors (see below), whose sum is σ = 125484660. Its totient is φ = 39836320.

The previous prime is 81664523. The next prime is 81664619. The reversal of 81664538 is 83546618.

It can be written as a sum of positive squares in 2 ways, for example, as 58171129 + 23493409 = 7627^2 + 4847^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Harshad number since it is a multiple of its sum of digits (41).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 81664495 and 81664504.

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, 497873 + ... + 498036.

Almost surely, 2^81664538 is an apocalyptic number.

81664538 is a deficient number, since it is larger than the sum of its proper divisors (43820122).

81664538 is a wasteful number, since it uses less digits than its factorization.

81664538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 995952.

The product of its digits is 138240, while the sum is 41.

The square root of 81664538 is about 9036.8433648039. The cubic root of 81664538 is about 433.8548963830.

The spelling of 81664538 in words is "eighty-one million, six hundred sixty-four thousand, five hundred thirty-eight".