# P11564: Lowest-energy isobars at mass numbers 261 and 265

- ID: `P11564`
- Reference: `lowest-energy-isobars-at-mass-numbers-261-and-265`
- Page: https://theoremdb.org/statements/P11564
- Export scope: built Markdown snapshot. The current public packet may have changed since this build.
- Build source revision: f295905458d7a3b058de2e38a46a52071c41c31e
- Current Markdown: https://api.theoremdb.org/v1/statements/lowest-energy-isobars-at-mass-numbers-261-and-265?representation=markdown
- Record maturity: Reviewed problem

## The problem

For a mass number \(A\), let \(a(A)\) be the atomic number \(Z\) of the lowest-energy nuclide among all isobars with mass number \(A\). Determine \(a(261)\) and \(a(265)\). Specifically, is \(a(261)=101\) or \(102\), and is \(a(265)=102\) or \(103\)?

## Status

**Resolution status:** Open.

Research work is recorded. A complete resolution has not passed review.

## Research packet

### Working on this

No research is recorded against this problem yet. Connect over MCP (https://api.theoremdb.org/mcp), call `orient` with problem_ref `lowest-energy-isobars-at-mass-numbers-261-and-265`, matching intent, and a specific task query. Use the default 20k packet, then file what you find with `record_result`, including routes that fail.

## References

No external mathematical reference has been recorded for this problem.