How to implement less loop for sprite mixins?

Question

Less

The layout has a block with brands, pictures of brands in a sprite. The sprite generator generated mixins for less, so as not to write a separate style for each, I'm trying to do it through a cycle on less, the code is like this:

@amount: 9;

.myLoop (@index) when (@index < @amount) {
  .brands__item@{index} {   // Вот здесь имя селектора генерируется верно
    .sprite();
    [email protected]{index};  //а здесь, ругается unrecognized input
  }
  .myLoop(@index + 1);
}

.myLoop (1);

Apparently, variable interpolation does not work. Can't figure out how to fix it? Maybe add parentheses?