81173509 has 4 divisors (see below), whose sum is σ = 84702816. Its totient is φ = 77644204.

The previous prime is 81173501. The next prime is 81173621. The reversal of 81173509 is 90537118.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81173509 - 2³ = 81173501 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 (81173501) 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, 1764619 + ... + 1764664.

It is an arithmetic number, because the mean of its divisors is an integer number (21175704).

Almost surely, 2^81173509 is an apocalyptic number.

It is an amenable number.

81173509 is a deficient number, since it is larger than the sum of its proper divisors (3529307).

81173509 is a wasteful number, since it uses less digits than its factorization.

81173509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3529306.

The product of its (nonzero) digits is 7560, while the sum is 34.

The square root of 81173509 is about 9009.6342323093. The cubic root of 81173509 is about 432.9835930825.

The spelling of 81173509 in words is "eighty-one million, one hundred seventy-three thousand, five hundred nine".