Given the data as
In[1]:= Clear[leDa]
leDa = {{0, 32400}, {513.354, 57600}, {1173.38, 90000}, {1980.08,
129600}, {2933.45, 176400}, {4033.5, 230400}, {5280.22,
291600}, {6673.61, 360000}, {8213.67, 435600}, {9900.41,
518400}, {11733.8, 608400}, {13713.9, 705600}, {15840.7,
810000}, {18114.1, 921600}, {20534.2, 1040400}, {23101.,
1166400}, {25814.4, 1299600}, {28674.5, 1440000}, {31681.3,
1587600}, {34834.8, 1742400}};
the differences in X and Y between a value and its predecessor are
In[3]:= {deltaX, deltaY} = (Rest[#] - Most[#]) & /@ Transpose[leDa]
Out[3]= {{513.354, 660.027, 806.7, 953.373, 1100.05, 1246.72, 1393.39,
1540.06, 1686.74, 1833.41, 1980.08, 2126.75, 2273.43, 2420.1,
2566.77, 2713.44, 2860.12, 3006.79, 3153.46}, {25200, 32400, 39600,
46800, 54000, 61200, 68400, 75600, 82800, 90000, 97200, 104400,
111600, 118800, 126000, 133200, 140400, 147600, 154800}}
What do you mean with a symbolic function about that? Should deltaX and deltaY considered separately?