81509559 has 8 divisors (see below), whose sum is σ = 108754560. Its totient is φ = 54302136.

The previous prime is 81509521. The next prime is 81509567. The reversal of 81509559 is 95590518.

It is a happy number.

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

It is not a de Polignac number, because 81509559 - 2⁷ = 81509431 is a prime.

It is a Smith number, since the sum of its digits (42) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 81509559.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81509579) 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, 3867 + ... + 13340.

It is an arithmetic number, because the mean of its divisors is an integer number (13594320).

Almost surely, 2^81509559 is an apocalyptic number.

81509559 is a deficient number, since it is larger than the sum of its proper divisors (27245001).

81509559 is a wasteful number, since it uses less digits than its factorization.

81509559 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18789.

The product of its (nonzero) digits is 81000, while the sum is 42.

The square root of 81509559 is about 9028.2644511556. The cubic root of 81509559 is about 433.5802729930.

The spelling of 81509559 in words is "eighty-one million, five hundred nine thousand, five hundred fifty-nine".