Chükö

Crossroads

A two-player game for one pack of 12 Chükö cards. Draft cards from a shared layout and build your own trail. Earn points by joining cards that share a prime factor, while watching what you leave for your opponent.

Setup

Shuffle the cards and deal them face up in three rows of four (4 × 3). Keep all cards visible. Leave space in front of each player for a trail, and use paper or counters to track points. Both players start at zero. Choose the first player at random.

A  B  C  D
E  F  G  H
I  J  K  L

The rows belong to both players. Only the leftmost remaining card in each row is available: initially A, E, and I. Taking a card makes the next card in that row available. Never rearrange the rows.

Play

Take turns choosing one available card. You must take a card on your turn; there is no passing.
Your first card starts your own trail and scores no points.
On every later turn, place your chosen card at either end of your own trail. If it shares at least one prime factor with the card at that end, score one point. Otherwise, score nothing; the move is still legal.
The new card becomes that end of your trail. Leave all previously played cards in place. You cannot insert a card in the middle, move cards, or play onto your opponent's trail.

A connection is worth only one point, even if the two cards share several factors. Only the end you play beside counts; matching both ends does not earn an extra point. For example, 6 and 15 match through their factor of 3, and 14 and 8 match through their factor of 2. Every pair of numbers shares 1 as a divisor, but 1 is not a prime factor and does not count as a match.

Example

Your trail is 6 — 15, and the available cards are 10, 7, and 9. You could take 10 and put it beside 15, scoring one point because they share a factor of 5:

6 — 15 — 10

You could instead put 10 beside 6 and score one point for their shared factor of 2. Either move scores the same, but leaves different numbers at the ends of your trail. Taking 7 would score nothing at either end, but might deny your opponent a match or prepare a future connection.

Winning

Stop when all 12 cards have been taken. Each player will have six cards and a score between zero and five. The higher score wins; equal scores are a draw. Cards are playing pieces, not stakes.

For a two-round match, note the starting layout before playing. After the first round, restore that exact layout and play again with the other player going first. Add each player's points from both rounds; the higher total wins. Equal totals are a draw.

Strategy

Consider both the card you take and the card you expose for your opponent. A point now may hand over an even more useful card. Keep different prime factors at your two ends to give yourself more matching choices. Sometimes taking a card for no points is worthwhile if it leaves a useful factor at an end or takes away your opponent's best option. All cards and both trails are visible, so you can plan ahead.