81861839 has 4 divisors (see below), whose sum is σ = 83406456. Its totient is φ = 80317224.

The previous prime is 81861803. The next prime is 81861869. The reversal of 81861839 is 93816818.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81861839 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81861839.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81861869) 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, 772229 + ... + 772334.

It is an arithmetic number, because the mean of its divisors is an integer number (20851614).

Almost surely, 2^81861839 is an apocalyptic number.

81861839 is a deficient number, since it is larger than the sum of its proper divisors (1544617).

81861839 is a wasteful number, since it uses less digits than its factorization.

81861839 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1544616.

The product of its digits is 82944, while the sum is 44.

The square root of 81861839 is about 9047.7532570246. The cubic root of 81861839 is about 434.2040122622.

The spelling of 81861839 in words is "eighty-one million, eight hundred sixty-one thousand, eight hundred thirty-nine".