"Nagarjuna on Mindfulness of the Buddha" consists of three extended passages from Bhikshu Dharmamitra's original annotated translations from Sino-Buddhist Classical Chinese of works written by Arya Nagarjuna (circa 150 CE).
All three of these passages have been selected from Tripitaka Master Kumarajiva's early Fifth Century Sanskrit-to-Chinese translations of works by Nagarjuna, as follows:
"The Easy Practice" -- Nagarjuna's Treatise on the Ten Grounds, Chapter 9;
"The Pratyutpanna Samadhi" -- Nagarjuna's Treatise on the Ten Grounds, Chapters 20-25; and
"Recollection of the Buddha" -- Nagarjuna's Exegesis on the Mahaprajnaparamita Sutra, Chapter 1, Part 36-1"