81591539 has 4 divisors (see below), whose sum is σ = 83131056. Its totient is φ = 80052024.

The previous prime is 81591533. The next prime is 81591541. The reversal of 81591539 is 93519518.

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-81591539 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81591496 and 81591505.

It is not an unprimeable number, because it can be changed into a prime (81591533) 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, 769679 + ... + 769784.

It is an arithmetic number, because the mean of its divisors is an integer number (20782764).

Almost surely, 2^81591539 is an apocalyptic number.

81591539 is a deficient number, since it is larger than the sum of its proper divisors (1539517).

81591539 is a wasteful number, since it uses less digits than its factorization.

81591539 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1539516.

The product of its digits is 48600, while the sum is 41.

The square root of 81591539 is about 9032.8034961467. The cubic root of 81591539 is about 433.7255851960.

The spelling of 81591539 in words is "eighty-one million, five hundred ninety-one thousand, five hundred thirty-nine".