I have seen this problem before, except it was worded differently. Is this the problem you wished to express?
1+4=5, 2+5=12, 3+6=21, 8+11=?
If so, then your answer is to simply add the last answer to the next problem. If not, then I am afraid I cannot help you.
1+4=5
5+2+5=12
12+3+6=21
21+8+11=40
