Sweet.
You inspired me to get my three-addend solution for 85709 down to around 0.05-0.06s, and only 15 active lines.
Thanks. Regarding the reported times, these are some details affecting the benchmarks:
1. The palindromes were supplied to the algorithm in a sorted vector. The time to create and sort them is not included.
2. Valid solutions are stored in pre-allocated memory. The time to write or display the solutions is not included.
3. The benchmarks were run on a PC with a Core-i3 with base 3.6 GHz clock.
4. Execution was within an Excel process, which limited utilization to one core of the four cores.
Since the aspect of increasing the number of addends is an extension of the well-studied "subset sum" problem, O(b^n) time using O(1) memory is the best known efficiency. There are Dynamic Programming approaches with O time using O memory that answer the question "how many groups of n palindromes adding up to the target value"? I have not yet come across any that actually list the unique groups with that efficiency.