81939659 has 4 divisors (see below), whose sum is σ = 83683104. Its totient is φ = 80196216.

The previous prime is 81939631. The next prime is 81939661. The reversal of 81939659 is 95693918.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81939659 - 2²⁴ = 65162443 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81939619) by changing a digit.

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, 871652 + ... + 871745.

It is an arithmetic number, because the mean of its divisors is an integer number (20920776).

Almost surely, 2^81939659 is an apocalyptic number.

81939659 is a deficient number, since it is larger than the sum of its proper divisors (1743445).

81939659 is a wasteful number, since it uses less digits than its factorization.

81939659 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1743444.

The product of its digits is 524880, while the sum is 50.

The square root of 81939659 is about 9052.0527506196. The cubic root of 81939659 is about 434.3415572410.

The spelling of 81939659 in words is "eighty-one million, nine hundred thirty-nine thousand, six hundred fifty-nine".