991021 has 8 divisors (see below), whose sum is σ = 1068320. Its totient is φ = 916272.

The previous prime is 991009. The next prime is 991027. The reversal of 991021 is 120199.

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 991021 - 2⁵ = 990989 is a prime.

It is the 996-th Hogben number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 990983 and 991001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991027) by changing a digit.

It is a nontrivial repunit in base 995.

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, 211 + ... + 1423.

It is an arithmetic number, because the mean of its divisors is an integer number (133540).

2⁹⁹¹⁰²¹ is an apocalyptic number.

It is an amenable number.

991021 is a deficient number, since it is larger than the sum of its proper divisors (77299).

991021 is a wasteful number, since it uses less digits than its factorization.

991021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1275.

The product of its (nonzero) digits is 162, while the sum is 22.

The square root of 991021 is about 995.5003766951. The cubic root of 991021 is about 99.6997996996.

The spelling of 991021 in words is "nine hundred ninety-one thousand, twenty-one".