81990909 has 96 divisors (see below), whose sum is σ = 167731200. Its totient is φ = 37169280.

The previous prime is 81990869. The next prime is 81990913. The reversal of 81990909 is 90909918.

It is not a de Polignac number, because 81990909 - 2⁹ = 81990397 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81990959) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 170932 + ... + 171410.

It is an arithmetic number, because the mean of its divisors is an integer number (1747200).

Almost surely, 2^81990909 is an apocalyptic number.

It is an amenable number.

81990909 is an abundant number, since it is smaller than the sum of its proper divisors (85740291).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81990909 is a wasteful number, since it uses less digits than its factorization.

81990909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 535 (or 532 counting only the distinct ones).

The product of its (nonzero) digits is 52488, while the sum is 45.

The square root of 81990909 is about 9054.8831577221. The cubic root of 81990909 is about 434.4320928285.

The spelling of 81990909 in words is "eighty-one million, nine hundred ninety thousand, nine hundred nine".