9999100021 has 4 divisors (see below), whose sum is σ = 10012742092. Its totient is φ = 9985457952.

The previous prime is 9999100009. The next prime is 9999100051. The reversal of 9999100021 is 1200019999.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1200019999 = 61 ⋅19672459.

It can be written as a sum of positive squares in 2 ways, for example, as 9646186225 + 352913796 = 98215^2 + 18786^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-9999100021 is a prime.

It is the 99996-th Hogben number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9999100051) by changing a digit.

It is a nontrivial repunit in base 99995.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6819936 + ... + 6821401.

It is an arithmetic number, because the mean of its divisors is an integer number (2503185523).

Almost surely, 2^9999100021 is an apocalyptic number.

It is an amenable number.

9999100021 is a deficient number, since it is larger than the sum of its proper divisors (13642071).

9999100021 is a wasteful number, since it uses less digits than its factorization.

9999100021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13642070.

The product of its (nonzero) digits is 13122, while the sum is 40.

The square root of 9999100021 is about 99995.5000037502. The cubic root of 9999100021 is about 2154.3700565603.

The spelling of 9999100021 in words is "nine billion, nine hundred ninety-nine million, one hundred thousand, twenty-one".