81691049209 has 16 divisors (see below), whose sum is σ = 101877350400. Its totient is φ = 63637382160.

The previous prime is 81691049201. The next prime is 81691049267. The reversal of 81691049209 is 90294019618.

It is a happy number.

It is not a de Polignac number, because 81691049209 - 2³ = 81691049201 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81691049201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 127842 + ... + 423940.

It is an arithmetic number, because the mean of its divisors is an integer number (6367334400).

Almost surely, 2^81691049209 is an apocalyptic number.

It is an amenable number.

81691049209 is a deficient number, since it is larger than the sum of its proper divisors (20186301191).

81691049209 is a wasteful number, since it uses less digits than its factorization.

81691049209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 299700.

The product of its (nonzero) digits is 279936, while the sum is 49.

The spelling of 81691049209 in words is "eighty-one billion, six hundred ninety-one million, forty-nine thousand, two hundred nine".