The Arapacana Alphabet
Other important sources include bas relief stone carving depicting scenes from the Lalitavistara Sūtra, and some engravings on the back of carvings.
The key source is the Pañcaviṃśatisāhasrikā Prajñāpāramita Sutra,
A is a door to the insight that all dharmas are unproduced from the very beginning (ādya-anutpannatvād);
RA is a door to the insight that all dharmas are without dirt (rajas);
PA is a door to the insight that all dharmas have been expounded in the ultimate sense (paramārtha);
CA is a door to the insight that the decrease (cyavana) or rebirth of any dharma cannot be apprehended, because all dharmas do not decrease, nor are they reborn;
NA is a door to the insight that the names [i.e. nāma) of all dharmas have vanished; the essential nature behind names cannot be gained or lost.
Across the various texts there is variation in the make up of the alphabet, the order, and the numberof letters.
Others may be scribal errors.
A complete explanations is still wanted.
The complete Arapacana Alphabet in the Pañcaviṃśatisāhasrikā: is a ra pa ca na la da ba ḍa ṣa va ta ya ṣṭa ka sa ma ga stha ja śva dha śa kha kṣa sta jña rta ha bha cha sma hva tsa bha ṭha ṇa pha ska ysa śca ṭa ḍha.
Other references to the Arapacana Alphabet
286 Pañcaviṃśatisāhasrikā Prajñāpāramita (trans. Dharmarakṣa) - T 222
291 Pañcaviṃśatisāhasrikā Prajñāpāramita (Mokṣa of Khotan) - T 221
404 Pañcaviṃśatisāhasrikā Prajñāpāramita (Kumārajīva) - T 223
402-406 Nāgārjuna's commentary on Prajñāpāramita (Kumārajīva) - T 1509
422 Avataṃsaka-sūtras (Buddhabhadra) - T 278
663 Collection of Prajñāpāramitas (Hsuang-tsang) - T 220
685 chapter of the Gaṇḍavyūha (Divākara) - T 295
699 Avataṃsaka-sūtras (Śikṣānanda) - T 279
746-771 chapter of the Gaṇḍavyūha (Amoghavajra) - T 1019, 1020 appendix
790 *Pratyanta-pālapati-dhāraṇī (Prājña and Muniśrī) - T 997
405-408 Dharmaguptaka Vinaya (trans. Buddhayaśas from Kabul and Chu Fo-nien) - T 1428.xi
716-735 (Śubhakarasiṃha) T 905,906
730 Pañcākṣara-mañjuśrī-hṛdaya-dhāraṇī (Vajrabodhi) - T 1173
Mañjuśrī-kalpa - T 1171
Pañcākṣara-mañjuśrī - T1172
Pañcākṣara-dhāraṇī - T1174