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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 10 |
| 4 | 75 |
| 5 | 508 |
| 6 | 3277 |
| 7 | 20566 |
| 8 | 126871 |
| 9 | 773688 |
| 10 | 4679769 |
| 11 | 28136546 |
| 12 | 168395235 |
| 13 | 1004239156 |
| 14 | 5971820709 |
| 15 | 35429993390 |
| 16 | 209800355631 |
| 17 | 1240361694064 |
| 18 | 7323260678065 |
| 19 | 43187703202234 |
| 20 | 254439363998587 |
| 21 | 1497730375793004 |
[0,0,1,10,75,508,3277,20566,126871,773688,4679769, 28136546,168395235,1004239156,5971820709, 35429993390,209800355631,1240361694064, 7323260678065,43187703202234,254439363998587, 1497730375793004] |