MathematicsMedium178×since 2002Q5329Let S_n = 1 . (n −-− 1) + 2 . (n −-− 2) + 3 . (n −-− 3) + ..... + (n −-− 1) . 1, n ≥\ge≥ 4. The sum ∑n=4∞(2Snn!−1(n−2)!)\sum\limits_{n = 4}^\infty {\left( {{{2{S_n}} \over {n!}} - {1 \over {(n - 2)!}}} \right)}n=4∑∞(n!2Sn−(n−2)!1) is equal to :Ae−13{{e - 1} \over 3}3e−1Be−26{{e - 2} \over 6}6e−2Ce3{e \over 3}3eDe6{e \over 6}6eCheck answerSkip