81991204 has 12 divisors (see below), whose sum is σ = 151925004. Its totient is φ = 38584064.

The previous prime is 81991201. The next prime is 81991229. The reversal of 81991204 is 40219918.

It can be written as a sum of positive squares in 2 ways, for example, as 39062500 + 42928704 = 6250^2 + 6552^2 .

It is a Harshad number since it is a multiple of its sum of digits (34).

It is a self number, because there is not a number n which added to its sum of digits gives 81991204.

It is not an unprimeable number, because it can be changed into a prime (81991201) 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 3 ways as a sum of consecutive naturals, for example, 602809 + ... + 602944.

It is an arithmetic number, because the mean of its divisors is an integer number (12660417).

Almost surely, 2^81991204 is an apocalyptic number.

It is an amenable number.

81991204 is a deficient number, since it is larger than the sum of its proper divisors (69933800).

81991204 is a wasteful number, since it uses less digits than its factorization.

81991204 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1205774 (or 1205772 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 34.

The square root of 81991204 is about 9054.8994472606. The cubic root of 81991204 is about 434.4326138510.

The spelling of 81991204 in words is "eighty-one million, nine hundred ninety-one thousand, two hundred four".