Написано на языке PascalABC.NET

1. const
2.    cValue = 2;
3. var
4.    N, i: integer;
5.    resultNumber: real;
6. begin
7.    Readln(N);
8.    
9.    for i := 1 to N do
10.        resultNumber := resultNumber + Power(cValue, i);
11.    Writeln(resultNumber);
12. end.