Official solution
(2.1P0
-- 3.2P1 + 4.3P2 .... up to
51th term)
+ (1! -- 2! + 3! -- ..... up to 51th term)
= ( 2.1! - 3.2! + 4.3! - ....+ 52.51!)
+ ( 1! -- 2! + 3! -- ..... + (51)! )
= (2! - 3! + 4! .....+ 52! )
+ ( 1! - 2! + 3! - 4! + .....+ 51! )
= 1 + (52)!