999989981 has 2 divisors, whose sum is σ = 999989982. Its totient is φ = 999989980.

The previous prime is 999989957. The next prime is 999990011. The reversal of 999989981 is 189989999.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 862303225 + 137686756 = 29365^2 + 11734^2 .

It is an emirp because it is prime and its reverse (189989999) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-999989981 is a prime.

It is a super-2 number, since 2×999989981² = 1999959924200760722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999989681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499994990 + 499994991.

It is an arithmetic number, because the mean of its divisors is an integer number (499994991).

Almost surely, 2^999989981 is an apocalyptic number.

It is an amenable number.

999989981 is a deficient number, since it is larger than the sum of its proper divisors (1).

999989981 is an equidigital number, since it uses as much as digits as its factorization.

999989981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34012224, while the sum is 71.

The square root of 999989981 is about 31622.6181869876. The cubic root of 999989981 is about 999.9966603222.

The spelling of 999989981 in words is "nine hundred ninety-nine million, nine hundred eighty-nine thousand, nine hundred eighty-one".