81166509 has 32 divisors (see below), whose sum is σ = 123863040. Its totient is φ = 52505136.

The previous prime is 81166507. The next prime is 81166513. The reversal of 81166509 is 90566118.

It is not a de Polignac number, because 81166509 - 2¹ = 81166507 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81166507) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 211732 + ... + 212114.

It is an arithmetic number, because the mean of its divisors is an integer number (3870720).

Almost surely, 2^81166509 is an apocalyptic number.

It is an amenable number.

81166509 is a deficient number, since it is larger than the sum of its proper divisors (42696531).

81166509 is a wasteful number, since it uses less digits than its factorization.

81166509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 606 (or 600 counting only the distinct ones).

The product of its (nonzero) digits is 12960, while the sum is 36.

The square root of 81166509 is about 9009.2457508939. The cubic root of 81166509 is about 432.9711466070.

The spelling of 81166509 in words is "eighty-one million, one hundred sixty-six thousand, five hundred nine".