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Eternity II

Eternity II:
the puzzle that beat everyone.

Eternity II looks like a children's jigsaw: 256 square pieces, match the colors. Launched in 2007 with a $2 million prize, it has never been solved: not by people, not by supercomputers, and it is not a scam. This site lets you feel why, right in your browser.

Start herePlay Eternity II onlineWhat is Eternity II?

A full 16×16 board, every edge matched and the border grey — this is what a solved Eternity II looks like. (It's a randomly generated board, not the official puzzle.)

Live right now

Lend a few CPU threads to the search

A community fleet is attacking the strict five-clue board right now, and it is short of machines. It has already carried the strict five-clue record from 460 to 465, and its dashboard shows what the fleet is doing this minute. The worker runs on Windows and Linux, uses only the threads you give it, and stops whenever you want.

Join the searchDownload the worker

Run by Benjamin Riotte, who holds the five-clue record. Follow the fleet on the live dashboard. No account, no reward: just the puzzle.

The Puzzle
256 pieces, 22 motifs, a $2 million prize nobody ever claimed. The full story and anatomy of Eternity II.
Playground
Solve a small one yourself, watch a real solver run at a million steps per second, or design its search path.
Algorithms
Backtracking, binary tricks and exponential walls: how computer scientists actually attack the puzzle, explained from scratch.
Board Viewer
Display and share any board. Fully compatible with e2.bucas.name links, including the famous 467/469/470 record boards.
Research
Papers, community records, solver internals, and an open lab notebook of attempts at the full 480.
For classrooms
Built for Terra Numerica: a hands-on way to discover combinatorial explosion, algorithms and why "simple-looking" can mean "impossibly hard". No prerequisites needed.