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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 120 |
| 5 | 665 |
| 6 | 3732 |
| 7 | 21153 |
| 8 | 120835 |
| 9 | 694590 |
| 10 | 4013088 |
| 11 | 23284424 |
| 12 | 135580865 |
| 13 | 791862354 |
| 14 | 4637009300 |
| 15 | 27215510265 |
| 16 | 160053426720 |
| 17 | 942939231825 |
| 18 | 5564024727096 |
| 19 | 32878367902380 |
| 20 | 194530139772844 |
| 21 | 1152303896900338 |
| 22 | 6832908809693304 |
| 23 | 40556775927067299 |
| 24 | 240938382783554100 |
[1,4,22,120,665,3732,21153,120835,694590,4013088, 23284424,135580865,791862354,4637009300, 27215510265,160053426720,942939231825, 5564024727096,32878367902380,194530139772844, 1152303896900338,6832908809693304, 40556775927067299,240938382783554100] |