Thanks for your help.
For other novice users:
    The complete solution is to convert the numeric variable in to text
variable with the text  function.
        EXECUTE ''INSERT INTO temp_tab VALUES(''
                        || quote_literal(nombre) ||'',''
                        || text(numero) ||'')'';
Conxita.
>How to construct an 'EXECUTE' sentence into a function using numeric
variables?
>To insert the variable in the string to execute, i use
'quote_literal(numero)' where numero is a numeric variable.
>When I execute the function, i get this message:
>
>    ERROR:  Function 'quote_literal(numeric)' does not exist
>              Unable to identify a function that satisfies the given argument
types
>              You may need to add explicit typecasts