28391220 has 144 divisors (see below), whose sum is σ = 101267712. Its totient is φ = 6347520.

The previous prime is 28391197. The next prime is 28391227. The reversal of 28391220 is 2219382.

It is a happy number.

It is a super-2 number, since 2×28391220² = 1612122746176800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (28391227) 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 47 ways as a sum of consecutive naturals, for example, 25189 + ... + 26291.

It is an arithmetic number, because the mean of its divisors is an integer number (703248).

Almost surely, 2^28391220 is an apocalyptic number.

28391220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 28391220, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (50633856).

28391220 is an abundant number, since it is smaller than the sum of its proper divisors (72876492).

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

28391220 is a wasteful number, since it uses less digits than its factorization.

28391220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1142 (or 1137 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 28391220 is about 5328.3412052908. The cubic root of 28391220 is about 305.0666162830.

The spelling of 28391220 in words is "twenty-eight million, three hundred ninety-one thousand, two hundred twenty".