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1

Part of 1981 Spain Mathematical Olympiad

Problems(1)

7 + 77 + 777 +...+ 7... 7

Source: Spanish Mathematical Olympiad 1981 P1

12/23/2022
Calculate the sum of nn addends 7+77+777+...+7...7.7 + 77 + 777 +...+ 7... 7.
Sumalgebra