( ( atomic ( mass number ) ) ( ( The sum ) ( of ( ( the number ) ( of protons ) ) ) ) )
(ROOT (NP (NP (JJ atomic) (JJ mass) (NN number)) (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS protons))))))))
atomic mass number The sum of the number of protons
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN in) (NP (DT the) (NN formula)))))))) (VP (VBZ is) (VP (VBN referred) (PP (TO to) (NP (RB as) (JJ molecular) (NN mass))))) (. .)))