81821539 has 8 divisors (see below), whose sum is σ = 84185360. Its totient is φ = 79491456.

The previous prime is 81821533. The next prime is 81821563. The reversal of 81821539 is 93512818.

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

It is a cyclic number.

It is not a de Polignac number, because 81821539 - 2⁹ = 81821027 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81821498 and 81821507.

It is not an unprimeable number, because it can be changed into a prime (81821533) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3474 + ... + 13255.

It is an arithmetic number, because the mean of its divisors is an integer number (10523170).

Almost surely, 2^81821539 is an apocalyptic number.

81821539 is a deficient number, since it is larger than the sum of its proper divisors (2363821).

81821539 is a wasteful number, since it uses less digits than its factorization.

81821539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16869.

The product of its digits is 17280, while the sum is 37.

The square root of 81821539 is about 9045.5259106367. The cubic root of 81821539 is about 434.1327487197.

The spelling of 81821539 in words is "eighty-one million, eight hundred twenty-one thousand, five hundred thirty-nine".