Question

$35168399728$

Answer 1

Here the rule which is applicable on the series: 35 168 399 728 is Rule A: Subtract twice the number from its square as:
$7^2-2\times 7=35,{14}^2-2\times 14=168,{21}^2-2\times 21=399and{28}^2-2\times 28=728$
Hence, Rule (A) is the correct answer.