81209105 has 4 divisors (see below), whose sum is σ = 97450932. Its totient is φ = 64967280.

The previous prime is 81209101. The next prime is 81209111. The reversal of 81209105 is 50190218.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8737936 + 72471169 = 2956^2 + 8513^2 .

It is not a de Polignac number, because 81209105 - 2² = 81209101 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81209101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8120906 + ... + 8120915.

It is an arithmetic number, because the mean of its divisors is an integer number (24362733).

Almost surely, 2^81209105 is an apocalyptic number.

It is an amenable number.

81209105 is a deficient number, since it is larger than the sum of its proper divisors (16241827).

81209105 is a wasteful number, since it uses less digits than its factorization.

81209105 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16241826.

The product of its (nonzero) digits is 720, while the sum is 26.

The square root of 81209105 is about 9011.6094566953. The cubic root of 81209105 is about 433.0468741202.

The spelling of 81209105 in words is "eighty-one million, two hundred nine thousand, one hundred five".