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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 43 |
| 5 | 163 |
| 6 | 656 |
| 7 | 2698 |
| 8 | 11344 |
| 9 | 48724 |
| 10 | 212399 |
| 11 | 939687 |
| 12 | 4195518 |
| 13 | 18895902 |
| 14 | 85815964 |
| 15 | 392491390 |
| 16 | 1804983326 |
| 17 | 8343871333 |
| 18 | 38761066926 |
| 19 | 180795136179 |
| 20 | 846325495536 |
| 21 | 3975432440478 |
| 22 | 18731970424992 |
| 23 | 88502758036004 |
| 24 | 419206009153425 |
| 25 | 1990366204167853 |
| 26 | 9470375008073564 |
| 27 | 45149095508017120 |
[1,1,4,12,43,163,656,2698,11344,48724,212399, 939687,4195518,18895902,85815964,392491390, 1804983326,8343871333,38761066926,180795136179, 846325495536,3975432440478,18731970424992, 88502758036004,419206009153425,1990366204167853, 9470375008073564,45149095508017120] |