In Jainism, the term "attam" (also spelled "aatam" or "āṭṭam") refers to the duration of time, specifically in the context of the lifespan of beings in hell (Naraka). According to Jain scriptures, one "attam" is the time it takes for the body of a god or a hell-being to decrease by the size of a single atom (paramāṇu).

However, your question seems to be about how many years are reduced by one attam in the lifespan of a hell-being. The Jain texts, especially in the Tattvartha Sutra and other canonical works, explain that:

• The lifespan in hell is measured in "sāgaropama" years (an extremely long duration).
• The reduction of lifespan in hell occurs gradually, and "one attam" is the duration in which the body is reduced by one atom, not a direct conversion to years.
• The actual reduction in years for one attam depends on the initial lifespan and body size of the hell-being, and is not a fixed number of years.

To summarize: One attam is not a fixed number of years, but a measure of time based on the reduction of the body by one atom. The number of years corresponding to one attam varies depending on the total lifespan and size of the being in hell.

If you would like more detailed scriptural references or further clarification from Jain texts, please let me know!