to anon


one bean scenario

1 -> 2 1st sec
2 -> 4 2nd sec
4 -> 8 3rd sec


two beans scenario

2 -> 4 1st sec
4 -> 8 2nd sec
8 -> 16 3rd sec

can you see it now?
for two beans scenario
you actually start from the 2nd of the 1st bean scenario
so you see, you actually only save one sec
which was used to multiply from ONE to TWO
i hope you see it now :)