Here is a very simple and pure Jain mantra for japa:

• Mantra (Prakrit): ॐ नमो अरिहंताणं
• Transliteration: Om Namo Arihantāṇam
• Meaning (arth): I bow to the Arihants — the enlightened beings who have conquered inner enemies like anger, pride, deceit, and greed.

How to do japa (simple way):

• Sit quietly with a straight spine, gently close your eyes.
• Breathe softly and repeat “Om Namo Arihantāṇam” with devotion.
• You may chant aloud or mentally, 108 times with a mālā, or for 5–10 minutes.
• Keep the mind focused on reverence and purity; avoid asking for material gains.

Notes in tradition:

• This is the first pāda of the sacred Navkār (Namokār) Mantra and is fully accepted in both Shvetāmbara and Digambara traditions.
• Its essence is bowing to the highest qualities, not to a person.

If you wish to expand your practice later, you can chant the full Navkār Mantra, but for simple daily japa this single line is perfect.