Javanese calendar as context to learn number pattern and least common multiple

This research is about to investigate how Javanese calendar and primbon could be used as context to learn number pattern, least common multiple and modular arithmetic for high school students. This article is the first step for the research, as this research only just reach preliminary stage at this point, which consist of validation on worksheet, one to one and small group to gain data about students' understandings regarding connection between contexts as student perception with mathematics learning which they had learned. This research using Realistic Mathematics Education (PMRI) approach. The problems which given in this research was based PISA framework. The methodology of this research is using Design Research. This research produce valid and practical problem, worksheet for learning material and support students to understand more about number pattern and least common multiple as basis to learn modular arithmetic even as the learning material itself only just enrichment in national curriculum.