81912109 has 2 divisors, whose sum is σ = 81912110. Its totient is φ = 81912108.

The previous prime is 81912071. The next prime is 81912121. The reversal of 81912109 is 90121918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 42536484 + 39375625 = 6522^2 + 6275^2 .

It is a cyclic number.

It is not a de Polignac number, because 81912109 - 2⁹ = 81911597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81912179) 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 as a sum of consecutive naturals, namely, 40956054 + 40956055.

It is an arithmetic number, because the mean of its divisors is an integer number (40956055).

Almost surely, 2^81912109 is an apocalyptic number.

It is an amenable number.

81912109 is a deficient number, since it is larger than the sum of its proper divisors (1).

81912109 is an equidigital number, since it uses as much as digits as its factorization.

81912109 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 31.

The square root of 81912109 is about 9050.5308684077. The cubic root of 81912109 is about 434.2928732403.

The spelling of 81912109 in words is "eighty-one million, nine hundred twelve thousand, one hundred nine".