Răspuns :
k! · k = k! · ( k +1 - 1 ) = k ! · ( k +1 ) - k! = ( k +1 ) ! - k !
k=1 = 2 ! - 1!
k=2 = 3 ! - 2 !
k =3 = 4! - 3!
...................................................
k =n -1 = n! - ( n-1 ) !
k=n = ( n+1 ) ! - n!
suma = ( n +1 ) ! -1
k=1 = 2 ! - 1!
k=2 = 3 ! - 2 !
k =3 = 4! - 3!
...................................................
k =n -1 = n! - ( n-1 ) !
k=n = ( n+1 ) ! - n!
suma = ( n +1 ) ! -1