81218109 has 16 divisors (see below), whose sum is σ = 127754240. Its totient is φ = 44912880.

The previous prime is 81218087. The next prime is 81218113. The reversal of 81218109 is 90181218.

It is not a de Polignac number, because 81218109 - 2¹⁵ = 81185341 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81218119) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 61729 + ... + 63030.

It is an arithmetic number, because the mean of its divisors is an integer number (7984640).

Almost surely, 2^81218109 is an apocalyptic number.

It is an amenable number.

81218109 is a deficient number, since it is larger than the sum of its proper divisors (46536131).

81218109 is a wasteful number, since it uses less digits than its factorization.

81218109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124800.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 81218109 is about 9012.1090206455. The cubic root of 81218109 is about 433.0628781137.

The spelling of 81218109 in words is "eighty-one million, two hundred eighteen thousand, one hundred nine".