81997789 has 2 divisors, whose sum is σ = 81997790. Its totient is φ = 81997788.

The previous prime is 81997781. The next prime is 81997823. The reversal of 81997789 is 98779918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 68062500 + 13935289 = 8250^2 + 3733^2 .

It is a cyclic number.

It is not a de Polignac number, because 81997789 - 2³ = 81997781 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81997781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40998894 + 40998895.

It is an arithmetic number, because the mean of its divisors is an integer number (40998895).

Almost surely, 2^81997789 is an apocalyptic number.

It is an amenable number.

81997789 is a deficient number, since it is larger than the sum of its proper divisors (1).

81997789 is an equidigital number, since it uses as much as digits as its factorization.

81997789 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2286144, while the sum is 58.

The square root of 81997789 is about 9055.2630552624. The cubic root of 81997789 is about 434.4442438066. Note that the first 3 decimals are identical.

The spelling of 81997789 in words is "eighty-one million, nine hundred ninety-seven thousand, seven hundred eighty-nine".