A red sideband cannot step below packet zero. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
At packet zero there is no lower motional packet
The checked packet index is 0, so a red sideband cannot remove one packet.
n=0⇒lower packet is out
The rejected red sideband still matches the energy relation
The drive energy is still 6 joules, but the accepted bit is 0.