There are over two billion direct line ancestors in our first 30 generations.
This chart was provided by Reed Richardson.

Number of                  Generations         Aprox.
 Direct Ancestors          Back                   Year
2                                     1                   1968
6                                     2                   1938
14                                   3                   1908
30                                   4                   1878
62                                   5                   1848
126                                 6                   1818
254                                 7                   1788
510                                 8                   1758
1022                               9                   1728
2,046                             10                  1698
4,094                             11                  1668
8,190                             12                  1638
16,382                           13                  1608
32,766                           14                  1578
65,534                           15                  1548
131,070                         16                  1518
262,142                         17                  1488
524,286                         18                  1458
1,048,574                      19                  1428
2,097,150                      20                  1398
4,194,302                      21                  1368
8,388,606                      22                  1338
16,777,214                    23                  1308
33,554,430                    24                  1278
67,108,862                    25                  1248
134,217,726                  26                  1218
268,435,454                  27                  1188
536,870,910                  28                  1158
1,073,741,822               29                  1128
2,147,483,646               30                  1098