81561839 has 4 divisors (see below), whose sum is σ = 81948600. Its totient is φ = 81175080.

The previous prime is 81561829. The next prime is 81561863. The reversal of 81561839 is 93816518.

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 81561839 - 2²⁰ = 80513263 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81561796 and 81561805.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81561829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 193064 + ... + 193485.

It is an arithmetic number, because the mean of its divisors is an integer number (20487150).

Almost surely, 2^81561839 is an apocalyptic number.

81561839 is a deficient number, since it is larger than the sum of its proper divisors (386761).

81561839 is a wasteful number, since it uses less digits than its factorization.

81561839 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 386760.

The product of its digits is 51840, while the sum is 41.

The square root of 81561839 is about 9031.1593386453. The cubic root of 81561839 is about 433.6729522336.

The spelling of 81561839 in words is "eighty-one million, five hundred sixty-one thousand, eight hundred thirty-nine".