Shousangen 「小三元」 is a standard yaku. This yaku employs the three sangenpai, where the hand is composed of two koutsu (triplet) and a jantou (pair) of the third type.

Shousangen
Type Yaku
Kanji 小三元
English Small three dragons
Value 2 han (Consider as 4 han)
Speed Medium
Difficulty Medium

Tile pattern

               agari :  

Winning on yasume (cheaper winning tile), notice that winning on   would give a daisangen yakuman instead.

Formation

Compatability

^ Ippatsu requires riichi to be of any use.

RCH DRI IPP^ SMO TAN PFU IPK ITT YAK SDJ SDO TOI SNA SNK CHA JUN RPK SSG HRO HON CHN CHI RIN HAI HOU CHK
SSG                                                  

Shousangen requires yakuhai, from the two groups of dragon tiles. Out of the regular four tile groups for a hand, two are dedicated for dragon tiles. So, this yaku has no room for the likes of ittsu, ryanpeikou, sanshoku, and sanshoku doukou. Each of those four yaku require at least three tile groups for their specific requirements. Naturally, tanyao and chinitsu are incompatible because of the dragon tiles.

Value

In general, this yaku is noted as 2 han. However, it is impossible for this yaku to score without two instances of yakuhai from the two groups of sangenpai. In combination, this yaku will never produce a hand worth less than 4 han. Even with both sangenpai groups called open, that is a combination of 8 fu; and then there's 2 more fu from the sangenpai pair of the third type. So, it does not take much for shousangen to score mangan. Just a simple, penchan, kanchan, or even tanki would suffice to take the hand into 40 fu.

External links

Shousangen in Japanese Wikipedia