991805221 has 8 divisors (see below), whose sum is σ = 1098118944. Its totient is φ = 888183120.

The previous prime is 991805209. The next prime is 991805251. The reversal of 991805221 is 122508199.

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

It is not a de Polignac number, because 991805221 - 2²³ = 983416613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991805201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 672130 + ... + 673603.

It is an arithmetic number, because the mean of its divisors is an integer number (137264868).

Almost surely, 2^991805221 is an apocalyptic number.

It is an amenable number.

991805221 is a deficient number, since it is larger than the sum of its proper divisors (106313723).

991805221 is a wasteful number, since it uses less digits than its factorization.

991805221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1345811.

The product of its (nonzero) digits is 12960, while the sum is 37.

The square root of 991805221 is about 31492.9392245309. The cubic root of 991805221 is about 997.2609112429.

It can be divided in two parts, 99180 and 5221, that added together give a palindrome (104401).

The spelling of 991805221 in words is "nine hundred ninety-one million, eight hundred five thousand, two hundred twenty-one".