Array
(
    [values] => Array
        (
            [0] => 18
            [1] => 19
            [2] => 110
        )
)

$formValues = isset($_GET['values']) ? $_GET['values'] : null;

if (!empty($formValues)) {
    foreach ($formValues as $key => $value) {
        echo "Semana {$key}<br>{$value}<br>";
    }
}

$formValues = isset($_GET['values']) ? $_GET['values'] : null;

if (!empty($formValues)) {
    $formValues = http_build_query($formValues);
}

setcookie('primeira_etapa', $formValues, (time() + (30 * 60))); //30 minutos de validade