81351809 has 18 divisors (see below), whose sum is σ = 104026482. Its totient is φ = 63386400.

The previous prime is 81351799. The next prime is 81351827. The reversal of 81351809 is 90815318.

It can be written as a sum of positive squares in only one way, i.e., 59290000 + 22061809 = 7700^2 + 4697^2 .

It is not a de Polignac number, because 81351809 - 2⁸ = 81351553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81351899) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 932 + ... + 12789.

It is an arithmetic number, because the mean of its divisors is an integer number (5779249).

Almost surely, 2^81351809 is an apocalyptic number.

It is an amenable number.

81351809 is a deficient number, since it is larger than the sum of its proper divisors (22674673).

81351809 is a wasteful number, since it uses less digits than its factorization.

81351809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13757 (or 13739 counting only the distinct ones).

The product of its (nonzero) digits is 8640, while the sum is 35.

The square root of 81351809 is about 9019.5237679159. The cubic root of 81351809 is about 433.3003816495.

The spelling of 81351809 in words is "eighty-one million, three hundred fifty-one thousand, eight hundred nine".