81355509 has 20 divisors (see below), whose sum is σ = 121813120. Its totient is φ = 54111240.

The previous prime is 81355493. The next prime is 81355541. The reversal of 81355509 is 90555318.

It is a happy number.

It is not a de Polignac number, because 81355509 - 2⁴ = 81355493 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81355609) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 45372 + ... + 47130.

It is an arithmetic number, because the mean of its divisors is an integer number (6090656).

Almost surely, 2^81355509 is an apocalyptic number.

It is an amenable number.

81355509 is a deficient number, since it is larger than the sum of its proper divisors (40457611).

81355509 is a wasteful number, since it uses less digits than its factorization.

81355509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2342 (or 2333 counting only the distinct ones).

The product of its (nonzero) digits is 27000, while the sum is 36.

The square root of 81355509 is about 9019.7288761913. The cubic root of 81355509 is about 433.3069505963.

The spelling of 81355509 in words is "eighty-one million, three hundred fifty-five thousand, five hundred nine".