81909904 has 40 divisors (see below), whose sum is σ = 162411480. Its totient is φ = 40009728.

The previous prime is 81909901. The next prime is 81909911. The reversal of 81909904 is 40990918.

It can be written as a sum of positive squares in 4 ways, for example, as 5382400 + 76527504 = 2320^2 + 8748^2 .

It is not an unprimeable number, because it can be changed into a prime (81909901) 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 7 ways as a sum of consecutive naturals, for example, 137832 + ... + 138424.

It is an arithmetic number, because the mean of its divisors is an integer number (4060287).

Almost surely, 2^81909904 is an apocalyptic number.

It is an amenable number.

81909904 is a deficient number, since it is larger than the sum of its proper divisors (80501576).

81909904 is a wasteful number, since it uses less digits than its factorization.

81909904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 787 (or 781 counting only the distinct ones).

The product of its (nonzero) digits is 23328, while the sum is 40.

The square root of 81909904 is about 9050.4090515291. The cubic root of 81909904 is about 434.2889762814.

The spelling of 81909904 in words is "eighty-one million, nine hundred nine thousand, nine hundred four".