Wrong answer given by a julia code for project euler 29

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I was trying to solve Project Euler Q.29 in julia and I am getting a wring answer.

Here is the problem statement:

Consider all integer combinations of ab for 2 ≤ a ≤ 5 and 2 ≤ b ≤ 5:

2^2=4, 2^3=8, 2^4=16, 2^5=32
3^2=9, 3^3=27, 3^4=81, 3^5=243
4^2=16, 4^3=64, 4^4=256, 4^5=1024
5^2=25, 5^3=125, 5^4=625, 5^5=3125
If they are then placed in numerical order, with any repeats removed, we get the following sequence of 15 distinct terms:

4, 8, 9, 16, 25, 27, 32, 64, 81, 125, 243, 256, 625, 1024, 3125

How many distinct terms are in the sequence generated by a^b for 2 ≤ a ≤ 100 and 2 ≤ b ≤ 100?

Here is my code, its pure brute force.

powers = []

n = 100

for a in collect(2:n)
    for b in collect(2:n)
        append!(powers,a^b)        
    end
end

length(unique(powers))

The correct answer is 9183 but I am getting 6143 as the answer.

Can someone please help me with this?

julia
1 Answers

You're suffering from integer overflow - see the manual here: 

julia> 2^62
4611686018427387904

julia> 2^63
-9223372036854775808

You can overcome the issue by using BigIntegers like so:

powers = []

n = 100

for a in collect(2:n)
    for b in collect(2:n)
        # note the `big()` here
        append!(powers,big(a)^b)        
    end
end

length(unique(powers))
user_24998920
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