ALGORITHM TO FIND SUM OF THE SERIES 1*5 - 2*7 + 3*9 - 4*11 ... UPTO N TERMS

STEP 1.      I <-- 1, J=5, Sum <-- 0, N <-- 0, Sign=1

STEP 2.      Read N

STEP 3.      While (I <= N)

        Begin

             Sum <-- Sum+  Sign*(I * J)

         J <-- J + 2

      I <-- I + 1

      Sign= Sign * (-1)

             End

STEP 4.      Print Sum