The complete pattern is: 512, 256, 128, 64, 32, 16, 8, ( and extended ) 4, 2, 1!
I do this pattern in my head literally all the time!
(16+5)4÷2=42
21×4÷2=42
84÷2=42
42=42
that is were to but you answer
That is true, I don,t quite know how to explain it but I just did this problem yesterday.