9987821 has 4 divisors (see below), whose sum is σ = 10014972. Its totient is φ = 9960672.

The previous prime is 9987793. The next prime is 9987827. The reversal of 9987821 is 1287899.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 3279721 + 6708100 = 1811^2 + 2590^2 .

It is a cyclic number.

It is not a de Polignac number, because 9987821 - 2²² = 5793517 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 (9987827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13016 + ... + 13761.

It is an arithmetic number, because the mean of its divisors is an integer number (2503743).

Almost surely, 2^9987821 is an apocalyptic number.

It is an amenable number.

9987821 is a deficient number, since it is larger than the sum of its proper divisors (27151).

9987821 is a wasteful number, since it uses less digits than its factorization.

9987821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27150.

The product of its digits is 72576, while the sum is 44.

The square root of 9987821 is about 3160.3514045118. The cubic root of 9987821 is about 215.3559706052.

It can be divided in two parts, 99878 and 21, that added together give a palindrome (99899).

The spelling of 9987821 in words is "nine million, nine hundred eighty-seven thousand, eight hundred twenty-one".