81981817 has 2 divisors, whose sum is σ = 81981818. Its totient is φ = 81981816.

The previous prime is 81981799. The next prime is 81981829. The reversal of 81981817 is 71818918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 72097081 + 9884736 = 8491^2 + 3144^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81981817 is a prime.

It is not a weakly prime, because it can be changed into another prime (81981917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40990908 + 40990909.

It is an arithmetic number, because the mean of its divisors is an integer number (40990909).

Almost surely, 2^81981817 is an apocalyptic number.

It is an amenable number.

81981817 is a deficient number, since it is larger than the sum of its proper divisors (1).

81981817 is an equidigital number, since it uses as much as digits as its factorization.

81981817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 32256, while the sum is 43.

The square root of 81981817 is about 9054.3810942549. The cubic root of 81981817 is about 434.4160341271.

The spelling of 81981817 in words is "eighty-one million, nine hundred eighty-one thousand, eight hundred seventeen".