<===> input.scss
h1:nth-of-type(#{2 + 'n + 1'}) {
    color: red;
}

h1:nth-of-type(#{2 + 'n   +  1'}) {
    color: red;
}

<===> output.css
h1:nth-of-type(2n + 1) {
  color: red;
}

h1:nth-of-type(2n + 1) {
  color: red;
}