999918001681 has 3 divisors (see below), whose sum is σ = 999919001641. Its totient is φ = 999917001722.

The previous prime is 999918001673. The next prime is 999918001699. The reversal of 999918001681 is 186100819999.

The square root of 999918001681 is 999959.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 999918001681 - 2³ = 999918001673 is a prime.

It is a super-2 number, since 2×999918001681² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (999918001651) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 499980 + ... + 1499938.

Almost surely, 2^999918001681 is an apocalyptic number.

999918001681 is the 999959-th square number.

999918001681 is the 499980-th centered octagonal number.

It is an amenable number.

999918001681 is a deficient number, since it is larger than the sum of its proper divisors (999960).

999918001681 is an frugal number, since it uses more digits than its factorization.

999918001681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1999918 (or 999959 counting only the distinct ones).

The product of its (nonzero) digits is 2519424, while the sum is 61.

The spelling of 999918001681 in words is "nine hundred ninety-nine billion, nine hundred eighteen million, one thousand, six hundred eighty-one".