421906 can be partitioned to 400000 + 20000 + 1000 + 900 + 00 + 6
The number 421906 is in between 400000 and 500000, but it's closer to 400000, so rounding to the nearest hundred thousand gives 400000
The number 421906 is in between 421000 and 422000, but it's closer to 422000, so the nearest thousand is 422000
