tokens: If you are willing to get into factorization , one could traverse the list , once from the left , factoring each number , hashing the index of each new prime ( with the prime as the key ) , updating the index of each prime already seen , and , of course , noting the nearest seen prime .
ner_tags: O O O O O O O O O O O O O B-Data_Structure O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O