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Let `P = sum_(r=1)^(50)(“”^(50+r)C_(r)(2r-1))/(“”^(50)C_(r)(50+r)), Q = sum_(r=0)^()(“”^(50)C_(r))^(2), R = sum_(0)^(100)(-1)^(r)(“”^(100)C_(r))^(2)`
If n is any positive integer, then find the number whose square is `ubrace(111……….1)_(“2 times”)-ubrace(222……….2)_(“n times”)`