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A003408 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 9 |
| 2 | 66 |
| 3 | 455 |
| 4 | 3060 |
| 5 | 20349 |
| 6 | 134596 |
| 7 | 888030 |
| 8 | 5852925 |
| 9 | 38567100 |
| 10 | 254186856 |
| 11 | 1676056044 |
| 12 | 11058116888 |
| 13 | 73006209045 |
| 14 | 482320623240 |
| 15 | 3188675231420 |
| 16 | 21094923659355 |
| 17 | 139646485582065 |
| 18 | 925029565741050 |
| 19 | 6131164307078475 |
| 20 | 40661170824914640 |
| 21 | 269807672771096460 |
[1,9,66,455,3060,20349,134596,888030,5852925, 38567100,254186856,1676056044,11058116888, 73006209045,482320623240,3188675231420, 21094923659355,139646485582065,925029565741050, 6131164307078475,40661170824914640, 269807672771096460] |