991220 has 24 divisors (see below), whose sum is σ = 2154600. Its totient is φ = 382592.

The previous prime is 991217. The next prime is 991223. The reversal of 991220 is 22199.

It is an interprime number because it is at equal distance from previous prime (991217) and next prime (991223).

It can be written as a sum of positive squares in 4 ways, for example, as 26896 + 964324 = 164^2 + 982^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991223) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 275 + ... + 1434.

It is an arithmetic number, because the mean of its divisors is an integer number (89775).

2⁹⁹¹²²⁰ is an apocalyptic number.

It is an amenable number.

991220 is an abundant number, since it is smaller than the sum of its proper divisors (1163380).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

991220 is a wasteful number, since it uses less digits than its factorization.

991220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1747 (or 1745 counting only the distinct ones).

The product of its (nonzero) digits is 324, while the sum is 23.

The square root of 991220 is about 995.6003214142. The cubic root of 991220 is about 99.7064725929.

The spelling of 991220 in words is "nine hundred ninety-one thousand, two hundred twenty".