Good! I do not know if I understood your question well ... But anyway, I tried to respond anyway ...
Possible is! after all in the computer everything is possible until you prove the contrary .... Well, let's go to what matters.
Solution
HTML
<head>
<script src="http://code.jquery.com/jquery-1.11.3.min.js"></script></head><body><divid="div_do_link">
<input type="text" name="input_quantidade" id="input_link"/>
<!-- Ancora-->
<a href="" id="ancora_link" >Link</a>
</div>
script
$("div#div_do_link #input_link").keyup(function(){
var value = this.value;
if(value){
var link = "https://sterilair.vtexcommercestable.com.br/checkout/cart/add?sku=17&qty="+value+"&seller=1&sc=1";
$('div#div_do_link a#ancora_link').attr('href',link);
}
})