1 , 1 , 3 , 9 , 5 , 25 , 7 , 49 _ , 81
"as seq is 1 , 1 , 3 , 9 , 5 , 25 , 7 , 49 9 , 81 two series are there . 1 , 3,5 , 7,9 . . . odd numbers and 1 , 9,25 , 49,81 . . square of odd numbers answer : d"
subtract(negate(9), multiply(subtract(1, 3), divide(subtract(1, 3), subtract(1, 1))))