Task: Question Generation
Input (English): The base of the stupa has 108 small depictions of the Dhyani Buddha Amitabha. It is surrounded with a brick wall with 147 niches, each with four or five prayer wheels engraved with the mantra, om mani padme hum. At the northern entrance where visitors must pass is a shrine dedicated to Ajima, the goddess of smallpox. Every year the stupa attracts many Tibetan Buddhist pilgrims who perform full body prostrations in the inner lower enclosure, walk around the stupa with prayer wheels, chant, and pray. Thousands of prayer flags are hoisted up from the top of the stupa downwards and dot the perimeter of the complex. The influx of many Tibetan refugees from China has seen the construction of over 50 Tibetan gompas (monasteries) around Boudhanath.
Output (English): What mantra is engraved on the stupa's prayer wheels?