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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 18 |
| 5 | 80 |
| 6 | 482 |
| 7 | 3280 |
| 8 | 26244 |
| 9 | 231148 |
| 10 | 2320130 |
| 11 | 25238348 |
| 12 | 302834694 |
| 13 | 3909539452 |
| 14 | 54761642704 |
| 15 | 816758411516 |
| 16 | 13076340876500 |
| 17 | 221396129723368 |
| 18 | 3985720881222850 |
| 19 | 75503196628737920 |
| 20 | 1510373288335622576 |
| 21 | 31634502738658957588 |
| 22 | 696162960370556156224 |
| 23 | 15978760340940405262668 |
[1,1,2,4,18,80,482,3280,26244,231148,2320130, 25238348,302834694,3909539452,54761642704, 816758411516,13076340876500,221396129723368, 3985720881222850,75503196628737920, 1510373288335622576,31634502738658957588, 696162960370556156224,15978760340940405262668] |