9215821 has 2 divisors, whose sum is σ = 9215822. Its totient is φ = 9215820.

The previous prime is 9215809. The next prime is 9215827. The reversal of 9215821 is 1285129.

9215821 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 5354596 + 3861225 = 2314^2 + 1965^2 .

It is an emirp because it is prime and its reverse (1285129) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 9215821 - 2²¹ = 7118669 is a prime.

9215821 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 9215821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9215827) 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 as a sum of consecutive naturals, namely, 4607910 + 4607911.

It is an arithmetic number, because the mean of its divisors is an integer number (4607911).

Almost surely, 2^9215821 is an apocalyptic number.

It is an amenable number.

9215821 is a deficient number, since it is larger than the sum of its proper divisors (1).

9215821 is an equidigital number, since it uses as much as digits as its factorization.

9215821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1440, while the sum is 28.

The square root of 9215821 is about 3035.7570719674. The cubic root of 9215821 is about 209.6579541416.

The spelling of 9215821 in words is "nine million, two hundred fifteen thousand, eight hundred twenty-one".