81809391 has 8 divisors (see below), whose sum is σ = 111739824. Its totient is φ = 53209280.

The previous prime is 81809363. The next prime is 81809411. The reversal of 81809391 is 19390818.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81809391 - 2⁵ = 81809359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81809291) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 332436 + ... + 332681.

It is an arithmetic number, because the mean of its divisors is an integer number (13967478).

Almost surely, 2^81809391 is an apocalyptic number.

81809391 is a deficient number, since it is larger than the sum of its proper divisors (29930433).

81809391 is a wasteful number, since it uses less digits than its factorization.

81809391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 665161.

The product of its (nonzero) digits is 15552, while the sum is 39.

The square root of 81809391 is about 9044.8543935212. The cubic root of 81809391 is about 434.1112625042. Note that the first 3 decimals are identical.

It can be divided in two parts, 8180 and 9391, that added together give a palindrome (17571).

The spelling of 81809391 in words is "eighty-one million, eight hundred nine thousand, three hundred ninety-one".