三角函數的作品

The triangular numbers are therefore 1, 1+2, 1+2+3, 1+2+3+4, ...,
Triangular number, is:
1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351,