S=112⋅22+522⋅32+732⋅42+.....up to n
S=22−1212⋅22+32−2222⋅32+42−3232⋅42+.....up to n
S=22−1212⋅22+32−2222⋅32+42−3232⋅42+.....up to n
S=2212⋅22−1212⋅22+3222⋅32−2222⋅32+4232⋅42−3232⋅42+.....up to n
S=1−1222+1222−1232+1232−1242+.....up to n
S=1.