$1^{2}\left(2^{2}+2^{2}\right)=3^{2}=(4-1)=3$

$2^{2}\left(3^{2}+6^{2}\right)=7^{2}=(9-2)=7$

$3^{2}\left(4^{2}+12^{2}\right)=13^{2}=(16-3)=13$

$6^{2}\left(7^{2}+42^{2}\right)=43^{2}=(49-6)=43$

$Ans:43^{2}$