Filling up the results of a query

Hello,

I could not find an answer for my following problem through Google,
maybe because I did not find the best keywords. So I hope that one of
you can help me.

I need to create a view that "fills up" the entries of a table.
Example: Let's consider a table t_rates with bank rates for borrowing
money for a certain duration:

Duration_Months; Rate
3; 4.0%
6; 4.5%
12; 4.8%

The problem is that I need a value for all durations, not only the
ones I have. So I would like to create a view that calculates (e.g.
interpolates, extrapolates) the rates. Result:

Duration_Months; Rate
1; 4.0%
2; 4.0%
3; 4.0%
4; 4.2%
5; 4.4%
6; 4.5%
....

Whatever the rates will be, that is not im****tant for me right now.
What I need is the sequence of all durations.

I could solve this through normal sql if I created an auxiliary table
t_numbers with a single column containing all the integer numbers I
needed and doing an outer join from t_numbers on t_rates. But I do not
like the idea of having such a dumb table t_numbers.

What is the best approach for my problem? Some form of "select from
dual"? Or PL / SQL?

Thanks.

Hans