8991221 has 4 divisors (see below), whose sum is σ = 9084012. Its totient is φ = 8898432.

The previous prime is 8991197. The next prime is 8991223. The reversal of 8991221 is 1221998.

It is a happy number.

8991221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 2283121 + 6708100 = 1511^2 + 2590^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-8991221 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8991223) 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, 46250 + ... + 46443.

It is an arithmetic number, because the mean of its divisors is an integer number (2271003).

Almost surely, 2^8991221 is an apocalyptic number.

It is an amenable number.

8991221 is a deficient number, since it is larger than the sum of its proper divisors (92791).

8991221 is an equidigital number, since it uses as much as digits as its factorization.

8991221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 92790.

The product of its digits is 2592, while the sum is 32.

The square root of 8991221 is about 2998.5364763498. The cubic root of 8991221 is about 207.9407267620.

The spelling of 8991221 in words is "eight million, nine hundred ninety-one thousand, two hundred twenty-one".