9999821 has 8 divisors (see below), whose sum is σ = 10796184. Its totient is φ = 9207360.

The previous prime is 9999761. The next prime is 9999823. The reversal of 9999821 is 1289999.

9999821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 4 ways, for example, as 45796 + 9954025 = 214^2 + 3155^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 9999821 - 2¹⁰ = 9998797 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9999823) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6551 + ... + 7931.

It is an arithmetic number, because the mean of its divisors is an integer number (1349523).

Almost surely, 2^9999821 is an apocalyptic number.

It is an amenable number.

9999821 is a deficient number, since it is larger than the sum of its proper divisors (796363).

9999821 is a wasteful number, since it uses less digits than its factorization.

9999821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1951.

The product of its digits is 104976, while the sum is 47.

The square root of 9999821 is about 3162.2493576567. The cubic root of 9999821 is about 215.4421835162.

The spelling of 9999821 in words is "nine million, nine hundred ninety-nine thousand, eight hundred twenty-one".