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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 36 |
| 6 | 116 |
| 7 | 382 |
| 8 | 1287 |
| 9 | 4420 |
| 10 | 15397 |
| 11 | 54264 |
| 12 | 193154 |
| 13 | 693374 |
| 14 | 2507288 |
| 15 | 9124560 |
| 16 | 33393355 |
| 17 | 122821380 |
| 18 | 453756765 |
| 19 | 1683107800 |
| 20 | 6265751310 |
| 21 | 23402516280 |
| 22 | 87670790155 |
| 23 | 329337229104 |
| 24 | 1240292449350 |
| 25 | 4681874312510 |
| 26 | 17711376176718 |
| 27 | 67135842263728 |
| 28 | 254956353358682 |
[1,1,2,4,12,36,116,382,1287,4420,15397,54264, 193154,693374,2507288,9124560,33393355,122821380, 453756765,1683107800,6265751310,23402516280, 87670790155,329337229104,1240292449350, 4681874312510,17711376176718,67135842263728, 254956353358682] |