$1^2=1$  

$2^2=4$  

$3^2=9$  

$4^2=16$  

$5^2=25$  

$6^2=36$  

$7^2=49$  

$8^2=64$  

$9^2=81$  

${10}^2=100$  

${11}^2=121$  

${12}^2=144$  

${13}^2=169$  

${14}^2=196$  

${15}^2=225$  

${16}^2=256$  

${17}^2=289$  

${18}^2=324$  

${19}^2=361$  

${20}^2=400$