9991221 has 8 divisors (see below), whose sum is σ = 13681824. Its totient is φ = 6480720.

The previous prime is 9991211. The next prime is 9991259. The reversal of 9991221 is 1221999.

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

It is not a de Polignac number, because 9991221 - 2¹¹ = 9989173 is a prime.

9991221 is a modest number, since divided by 1221 gives 999 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9991211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44895 + ... + 45116.

It is an arithmetic number, because the mean of its divisors is an integer number (1710228).

Almost surely, 2^9991221 is an apocalyptic number.

It is an amenable number.

9991221 is a deficient number, since it is larger than the sum of its proper divisors (3690603).

9991221 is a wasteful number, since it uses less digits than its factorization.

9991221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90051.

The product of its digits is 2916, while the sum is 33.

The square root of 9991221 is about 3160.8892736064. The cubic root of 9991221 is about 215.3804046044.

The spelling of 9991221 in words is "nine million, nine hundred ninety-one thousand, two hundred twenty-one".