is 2 , open or closed. You hold three triplets built from your own draws. The fourth set can be a call.
The name players use is sanankou (三暗刻). This site's glossary also lists it as Three Concealed Triplets. The EMA 2016 rules call it three concealed pungs.
What counts as concealed
A triplet is concealed when every tile in it came from your own draws. A is open. A closed still counts, because the EMA entry accepts concealed kongs.
The catch is the last tile. A triplet you finish with a discard counts as open. Tenhou's rules say so directly: a triplet completed by is an open triplet.
Two concealed triplets are done: 2 man and 4 pin. The hand waits on or , a wait on two pairs. Every tile is 2 through 8, so the hand is also tanyao.
Draw yourself and the 6 pin triplet is concealed too. That's sanankou, , and menzen tsumo: 4 han. The fu are the base 20, plus 2 for the tsumo, plus 4 for each closed simple triplet. 34 rounds up to 40, and 4 han 40 fu is paid as a . A collects 2,000 from each other non-dealer and 4,000 from the dealer.
Win the same tile by ron and the 6 pin triplet counts as open. Two concealed triplets aren't sanankou, so the hand is tanyao alone. The fu are 20, plus 10 for a closed ron, plus 4 and 4 for the closed triplets, plus 2 for the open one: 40. At 1 han 40 fu, a non-dealer collects 1,300. The dealer collects 2,000. The 8 sou works the same way.
Those payments have no , no , and no sticks. The scoring guide lists every triplet's fu.
The glossary entry is the short form: three triplets formed without calling, 2 han, and the fourth set can be open.
Open or closed
Tenhou's yaku list puts sanankou at 2 han and doesn't mark it as losing a han after a call. The EMA 2016 rules file it with the 2 fan yaku and add that the whole hand doesn't have to be concealed. Their fifth scoring example is a of four triplets won on a discard. The triplet the discard finished isn't counted as concealed, so the hand scores three concealed pungs, not four. That's the row on this site: 2 han, open or closed.
Sanankou with a call
You called on 345 sou: . These ten tiles are still in your hand.
Three triplets are concealed: 2 man, 6 pin, and 8 sou. The hand waits on or 
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pairs the lone 4 pin. All three triplets stay concealed, so the open hand still scores sanankou, plus tanyao: 3 han. The fu are the base 20, plus 4 for each closed simple triplet, plus 2 for the . 34 rounds up to 40. At 3 han 40 fu, a non-dealer ron collects 5,200. The dealer collects 7,700.
makes 456 pin and leaves 6 pin as the pair. The 6 pin triplet is gone, so the hand is tanyao alone. The fu are 20, plus 4 and 4 for the two triplets left, plus 2 for the : 30. At 1 han 30 fu, a non-dealer ron collects 1,000. The dealer collects 1,500.
Four of them
is suuankou, a yakuman. A closed hand of four triplets on a wait on two pairs is sanankou on a ron and suuankou on a tsumo. The toitoi page walks through that hand.
Common mistakes
- Counting a ron triplet as concealed. The triplet the discard finishes is open.
- Counting a pon. A called triplet is open from the start.
- Dropping the yaku after a call. The fourth set can be a chi or a pon.
- Missing the tsumo. On a wait on two pairs, a tsumo can score sanankou where a ron on the same tile can't.
What sits with it
Toitoi fits when the fourth set is a triplet too. Tanyao fits when every tile is 2 through 8, as in both hands here. Yakuhai fits when one of the triplets is a dragon, your , or the .
Price a sanankou hand
The score calculator turns 3 han 40 fu, an open sanankou with tanyao, into 5,200 or 7,700. A closed one with tanyao and a tsumo is a mangan.
Open the score calculator