gistfile1.sass

@for $n from 1 through 7
  #plantilla-#{$n}
    :left 7em*$n
    :-webkit-transform rotate(10deg*$n/(1.61803399*$n*$n))

Good stuff! Here's how it would look if you used the Compass rotate helper. Also note the location of the colon. You are using the OLD Sass syntax.

@import "compass"

@for $n from 1 through 7
  #plantilla-#{$n}
    $rotation: 10 * ($n / (1.61803399 * $n * $n))
    left: 7em * $n
    +rotate(#{$rotation}deg)

... with this as the output:

#plantilla-1 {
  left: 7em;
  -moz-transform: rotate(6.18deg);
  -webkit-transform: rotate(6.18deg);
  -o-transform: rotate(6.18deg);
  -ms-transform: rotate(6.18deg);
  transform: rotate(6.18deg);
}

#plantilla-2 {
  left: 14em;
  -moz-transform: rotate(3.09deg);
  -webkit-transform: rotate(3.09deg);
  -o-transform: rotate(3.09deg);
  -ms-transform: rotate(3.09deg);
  transform: rotate(3.09deg);
}

#plantilla-3 {
  left: 21em;
  -moz-transform: rotate(2.06deg);
  -webkit-transform: rotate(2.06deg);
  -o-transform: rotate(2.06deg);
  -ms-transform: rotate(2.06deg);
  transform: rotate(2.06deg);
}

#plantilla-4 {
  left: 28em;
  -moz-transform: rotate(1.545deg);
  -webkit-transform: rotate(1.545deg);
  -o-transform: rotate(1.545deg);
  -ms-transform: rotate(1.545deg);
  transform: rotate(1.545deg);
}

#plantilla-5 {
  left: 35em;
  -moz-transform: rotate(1.236deg);
  -webkit-transform: rotate(1.236deg);
  -o-transform: rotate(1.236deg);
  -ms-transform: rotate(1.236deg);
  transform: rotate(1.236deg);
}

#plantilla-6 {
  left: 42em;
  -moz-transform: rotate(1.03deg);
  -webkit-transform: rotate(1.03deg);
  -o-transform: rotate(1.03deg);
  -ms-transform: rotate(1.03deg);
  transform: rotate(1.03deg);
}

#plantilla-7 {
  left: 49em;
  -moz-transform: rotate(0.883deg);
  -webkit-transform: rotate(0.883deg);
  -o-transform: rotate(0.883deg);
  -ms-transform: rotate(0.883deg);
  transform: rotate(0.883deg);
}

For some reason, the old syntax feels more natural to me. But I didn't know it was considered old. Does it affects the performance?

Don't think so, but it's been deprecated so one day support for it might drop and you'd have to update all your codes :(

Oh, crap. Thanks for the update then. :B