Recursive definitions (Un=Un-1+x) acceptable for general statements (portfolio)?

[Yoni Pinto]

When finding general statements, are recursive definitions acceptable? I didn't use a calculator or excel to find the general statements but they are recursive definitions (U_n=U_n-1 + x kind of definitions). Would it be a problem if my general statements were of this kind?

[Neko_K]

Yes, you certainly can use recursive definitions for general statements. I think it is usually specified in the task paper if they want you to find the nth term with a specific polynomial expression, but if it just asks for the general statement without noting any other additional info then I see no problem for using recursive definitions. When simple series or sequences, or other obvious polynomial expressions are not used, recursive definitions are quite viable if you have a certain set of results.

In fact, I used recursive definitions for my general statements in the Stellar Numbers portfolio last year and got 19!