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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 16 |
| 5 | 41 |
| 6 | 108 |
| 7 | 280 |
| 8 | 729 |
| 9 | 1908 |
| 10 | 4969 |
| 11 | 12950 |
| 12 | 33796 |
| 13 | 88112 |
| 14 | 229740 |
| 15 | 599191 |
| 16 | 1562470 |
| 17 | 4074372 |
| 18 | 10625188 |
| 19 | 27707446 |
| 20 | 72253034 |
| 21 | 188417568 |
| 22 | 491341657 |
| 23 | 1281284446 |
| 24 | 3341248089 |
| 25 | 8713071846 |
| 26 | 22721332009 |
| 27 | 59251115518 |
| 28 | 154510913809 |
[1,2,6,16,41,108,280,729,1908,4969,12950,33796, 88112,229740,599191,1562470,4074372,10625188, 27707446,72253034,188417568,491341657,1281284446, 3341248089,8713071846,22721332009,59251115518, 154510913809] |