Chapter 7 - Periodic Properties of the Elements - Exercises - Page 291: 7.9a

$2\times1=2$ $2\times(1+3)=8$ $2\times(1+3+5)=18$ $2\times(1+3+5+7)=32$

This question only needs to be dealt with by mathematical calculations. $2\times1=2$ $2\times(1+3)=2\times4=8$ $2\times(1+3+5)=2\times9=18$ $2\times(1+3+5+7)=2\times16=32$