<![CDATA[The integration of cultural knowledge systems into mathematics education remains underexplored, particularly within Indonesian coastal communities, where traditional practices are deeply intertwined with environmental and astronomical phenomena. Although ethnomathematics has received increasing scholarly attention, there is a notable lack of empirical studies that illuminate the mathematical reasoning embedded in indigenous calendar systems—especially those employed by coastal communities for subsistence activities. This study addresses that gap by investigating the ethnomathematical knowledge inherent in the calendrical system used by villagers in the Lungkak community of East Lombok, Indonesia. It highlights a unique integration of the Pupuru (known as the Pleiades star cluster), lunar phases, the Hijri calendar, and the Gregorian calendar to predict seasonal transitions and tidal patterns essential to fishing practices. Adopting an ethnographic approach to comprehensively explore cultural dynamics and social phenomena within the community, data were collected through purposive sampling, in-depth interviews, participant observation, and document analysis, and subsequently analyzed using interactive ethnographic methods. The findings reveal the existence of sophisticated mathematical constructs within the community’s calendrical practices, including trigonometric reasoning (angular positioning of celestial bodies), numerical and arithmetic sequences (patterns of star and lunar visibility), modular arithmetic (cyclical forecasting of astronomical events), and set theory (classification of tidal phases). These results demonstrate the community’s implicit engagement with formal mathematical concepts through culturally embedded knowledge. This study contributes to the advancement of culturally responsive mathematics education by advocating for the integration of ethnomathematical content into classroom instruction. Such integration enhances students’ mathematical literacy, contextual relevance, and engagement with mathematical learning.]]>
