81111509 has 4 divisors (see below), whose sum is σ = 81161004. Its totient is φ = 81062016.

The previous prime is 81111451. The next prime is 81111529. The reversal of 81111509 is 90511118.

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

It can be written as a sum of positive squares in 2 ways, for example, as 62362609 + 18748900 = 7897^2 + 4330^2 .

It is a cyclic number.

It is not a de Polignac number, because 81111509 - 2¹² = 81107413 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81111529) 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, 22202 + ... + 25595.

It is an arithmetic number, because the mean of its divisors is an integer number (20290251).

Almost surely, 2^81111509 is an apocalyptic number.

It is an amenable number.

81111509 is a deficient number, since it is larger than the sum of its proper divisors (49495).

81111509 is a wasteful number, since it uses less digits than its factorization.

81111509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49494.

The product of its (nonzero) digits is 360, while the sum is 26.

The square root of 81111509 is about 9006.1928138365. The cubic root of 81111509 is about 432.8733279615.

The spelling of 81111509 in words is "eighty-one million, one hundred eleven thousand, five hundred nine".