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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 2 |
| 4 | 4 |
| 5 | 16 |
| 6 | 38 |
| 7 | 104 |
| 8 | 456 |
| 9 | 1600 |
| 10 | 6154 |
| 11 | 29952 |
| 12 | 131660 |
| 13 | 644736 |
| 14 | 3516334 |
| 15 | 18383616 |
| 16 | 106736272 |
| 17 | 645554176 |
| 18 | 3902982930 |
| 19 | 25645936640 |
| 20 | 170222268308 |
| 21 | 1160636121088 |
| 22 | 8352824699446 |
| 23 | 60217271582720 |
| 24 | 450765801976408 |
[0,1,2,2,4,16,38,104,456,1600,6154,29952,131660, 644736,3516334,18383616,106736272,645554176, 3902982930,25645936640,170222268308,1160636121088, 8352824699446,60217271582720,450765801976408] |