it seems to me that after the fifth element, future elements seem to be generated based on one of a few operations. a general description of the sequence may be seen as follows: replace the lonely blue node (with nothing branching from it) with a chain of two blue nodes, then remove them and replace them with several green nodes branching from the starting node. then continue by removing nodes. at some point, stop removing nodes, and start again with a green node with blue nodes branching from it with each of which (except one) has a green node coming from it. continue as before, except at some point add as many blue nodes as possible (still possibly retaining some green nodes branching from blue nodes). continue as previously. I do also spot the error with the last three elements of the shown sequence having one too many blue nodes. I expect the next element of the sequence to be the last one shown, minus one green node, and perhaps it would continue like before with this repeated green node trick. it is however, unclear when to diversify into many branches and when to stop removing nodes. I might wonder how long the sequence would be if you were forced to use the maximum number of nodes at each step (this is relevant to a puzzle I know of, on the confounding calendar) I expect the total would be significantly reduced considering how many steps are done by removing nodes.