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A006819 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 30 |
| 3 | 150 |
| 4 | 750 |
| 5 | 3726 |
| 6 | 18438 |
| 7 | 90966 |
| 8 | 447918 |
| 9 | 2201622 |
| 10 | 10809006 |
| 11 | 52999446 |
| 12 | 259668942 |
| 13 | 1271054982 |
| 14 | 6218232414 |
| 15 | 30399142614 |
[1,6,30,150,750,3726,18438,90966,447918,2201622, 10809006,52999446,259668942,1271054982,6218232414, 30399142614] |