[" (i) "5+55+555+..." ."],[" Find the "20^(" th ")" term of the series "2times4+4times6+6times8+...+n" terms."],[" Find the sum of the first "n" terms of the series: "3+7+13+21+31+..],[" 24.If "S_(.)S_(.)" .are the sum of first "n" natural numbers,their squares and "]