i just need to swap to number

i try it on REPL and some thing weird is happen

```
function highestValuePalindrome(s, n, k)
temp = Array{Int64}(undef,n)
j=1
for i in s
println(i) # here i =3
temp[j] = i # i is 3 right ? why he put the number 51 ?
j+=1
println(temp)
end
end
s = "3493"
k=1
n=4
println("Total pairs " ,highestValuePalindrome(s, n, k))
```

the final output is `[51, 52, 57, 51]`

what is this number ?