數與數線(1)
Author: 藍邦偉　老師

$ ∵\frac{1}{7}=0.\overline{142857}⇒\frac{4}{7}=0.\overline{571428} $

$ f(1)+f(2)+...+f(123)  $

$ =\left [ f(1)+f(2)+...+f(6) \right ]+...+\left [ f(115)+...+f(120) \right ]+f(121)+f(122)+f(123)  $

=\left [ 5+7+1+4+2+8 \right ] +...+\left [  5+7=1+4+2+8\right ] +5+7+1

$ =27×20+13=553 $

n = 0 (slider from 0 to 5, step 1)