Due to the difcult educational condition caused by the COVID-19 pandemic, the design and development of mobile phone apps and technologies for teaching and learning are being more considered. Moreover, technology-based infrastructure for the use of distance education is developing rapidly. In this paper, an Android application called Triangular App (TriApp) was designed for teaching multiplication to preschool children. This application uses the Triple Multiplication method in which three numbers (including two numbers, and the product of multiplication of these two numbers) are considered as a group. By repeating and memorizing this group, if any of the numbers are not displayed, the child can guess the missed number. With TriApp, in addition to multiplication, children can also learn division. There is a test and competition section in which the child receives points by giving the correct answers, which increases the children's desire to learn. To evaluate the efectiveness of the TriApp, two preschool children groups were examined in 10 days. The former learned multiplication using TriApp and the later learned it using the multiplication table (repeated additions). The results showed that during test, 100% of the children that used the TriApp could answer asked multiplications correctly and only 40–70% of the children who were trained through multiplication table could answer asked multiplications correctly. Also, the children were satisfed 94% with the application, whereas, they were satisfed only 60% with the multiplication table. This mobile application was developed using Java programming language, Eclipse IDE, and SQLite database.
