81115731209 has 4 divisors (see below), whose sum is σ = 85384980240. Its totient is φ = 76846482180.

The previous prime is 81115731197. The next prime is 81115731211. The reversal of 81115731209 is 90213751118.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 90213751118 = 2 ⋅45106875559.

It is a cyclic number.

It is not a de Polignac number, because 81115731209 - 2²⁰ = 81114682633 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81115731409) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2134624487 + ... + 2134624524.

It is an arithmetic number, because the mean of its divisors is an integer number (21346245060).

Almost surely, 2^81115731209 is an apocalyptic number.

It is an amenable number.

81115731209 is a deficient number, since it is larger than the sum of its proper divisors (4269249031).

81115731209 is a wasteful number, since it uses less digits than its factorization.

81115731209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4269249030.

The product of its (nonzero) digits is 15120, while the sum is 38.

The spelling of 81115731209 in words is "eighty-one billion, one hundred fifteen million, seven hundred thirty-one thousand, two hundred nine".