9917821 has 4 divisors (see below), whose sum is σ = 10148512. Its totient is φ = 9687132.

The previous prime is 9917779. The next prime is 9917827. The reversal of 9917821 is 1287199.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 9917821 - 2⁹ = 9917309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9917827) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 115281 + ... + 115366.

It is an arithmetic number, because the mean of its divisors is an integer number (2537128).

Almost surely, 2^9917821 is an apocalyptic number.

It is an amenable number.

9917821 is a deficient number, since it is larger than the sum of its proper divisors (230691).

9917821 is a wasteful number, since it uses less digits than its factorization.

9917821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 230690.

The product of its digits is 9072, while the sum is 37.

The square root of 9917821 is about 3149.2572140109. The cubic root of 9917821 is about 214.8516806501.

It can be divided in two parts, 99178 and 21, that added together give a palindrome (99199).

The spelling of 9917821 in words is "nine million, nine hundred seventeen thousand, eight hundred twenty-one".