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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 52 |
| 5 | 221 |
| 6 | 1019 |
| 7 | 4818 |
| 8 | 23522 |
| 9 | 117209 |
| 10 | 594789 |
| 11 | 3062414 |
| 12 | 15966168 |
| 13 | 84132345 |
| 14 | 447457816 |
| 15 | 2399177028 |
| 16 | 12956403904 |
| 17 | 70416558196 |
| 18 | 384897011042 |
| 19 | 2114694606220 |
| 20 | 11672750655842 |
| 21 | 64705139473661 |
| 22 | 360068911514032 |
| 23 | 2010827078176568 |
[1,4,12,52,221,1019,4818,23522,117209,594789, 3062414,15966168,84132345,447457816,2399177028, 12956403904,70416558196,384897011042, 2114694606220,11672750655842,64705139473661, 360068911514032,2010827078176568] |