9991021 has 8 divisors (see below), whose sum is σ = 10418688. Its totient is φ = 9570000.

The previous prime is 9990997. The next prime is 9991027. The reversal of 9991021 is 1201999.

9991021 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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

It is a cyclic number.

It is not a de Polignac number, because 9991021 - 2⁵ = 9990989 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9991027) 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 7 ways as a sum of consecutive naturals, for example, 1536 + ... + 4726.

It is an arithmetic number, because the mean of its divisors is an integer number (1302336).

Almost surely, 2^9991021 is an apocalyptic number.

It is an amenable number.

9991021 is a deficient number, since it is larger than the sum of its proper divisors (427667).

9991021 is a wasteful number, since it uses less digits than its factorization.

9991021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3323.

The product of its (nonzero) digits is 1458, while the sum is 31.

The square root of 9991021 is about 3160.8576367815. The cubic root of 9991021 is about 215.3789674638.

The spelling of 9991021 in words is "nine million, nine hundred ninety-one thousand, twenty-one".