999643681 has 2 divisors, whose sum is σ = 999643682. Its totient is φ = 999643680.

The previous prime is 999643669. The next prime is 999643691. The reversal of 999643681 is 186346999.

999643681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 998560000 + 1083681 = 31600^2 + 1041^2 .

It is a cyclic number.

It is not a de Polignac number, because 999643681 - 2⁷ = 999643553 is a prime.

It is a super-3 number, since 3×999643681³ (a number of 28 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is not a weakly prime, because it can be changed into another prime (999643621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499821840 + 499821841.

It is an arithmetic number, because the mean of its divisors is an integer number (499821841).

Almost surely, 2^999643681 is an apocalyptic number.

It is an amenable number.

999643681 is a deficient number, since it is larger than the sum of its proper divisors (1).

999643681 is an equidigital number, since it uses as much as digits as its factorization.

999643681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2519424, while the sum is 55.

The square root of 999643681 is about 31617.1422016602. The cubic root of 999643681 is about 999.8812128902.

It can be divided in two parts, 999 and 643681, that added together give a triangular number (644680 = T₁₁₃₅).

The spelling of 999643681 in words is "nine hundred ninety-nine million, six hundred forty-three thousand, six hundred eighty-one".