// Read ith byte
recfun ith(arr, i) {
  if i == 0 { arr%16 } else { ith(arr/16,i-1) }
}
// Encode
fun arr3(x0,x1,x2) {
  (x0 + (x1*16)) + (x2*256)
}
ith(15,0) == 15
ith(18,0) == 2
ith(18,1) == 1
ith(arr3(3,5,7),0) == 3
ith(arr3(3,5,7),1) == 5
//ith(arr3(3,5,7),2) == 7
//ith(arr3(3,5,7),3) == 0