Fulltext doesn´t work for integer?

I have used the following code:

a1 = “+”
a2 = “"
@searchstring = params[:searching].gsub(" ", "
+”)
@results = Product.find_by_sql(“SELECT * FROM products WHERE MATCH
(name,sku) AGAINST (’”+a1+@searchstring+a2+"’ IN BOOLEAN MODE) order by
name desc LIMIT 0,50;")

It works, BUT not for numbers. Any idea why it coesn´t work for numbers?
If I have example: “this is 34” in the database. It works fine “this
is”, but as soon as I enter the “34” it shows no results.

Thanks,

Mark