Wahyuni, IrmaMashadi, Mashadi2019-04-232019-04-232019-04-23wahyu sari yenihttps://repository.unri.ac.id/handle/123456789/9658This articel discusses some development of numbers and series on triangular number. Then the development of numbers and series on triangular number involved in this study are the sum and difference in triangular number, the difference in the square of the triangular number, the sum of triangular number and the sum of the sum of triangular numbers. These are proved directly and using the concept of mathematical induction.enTriangular numberodd triangular numberseven triangular numberseven triangular numbersArticle