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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 16 |
| 4 | 40 |
| 5 | 105 |
| 6 | 273 |
| 7 | 715 |
| 8 | 1870 |
| 9 | 4896 |
| 10 | 12816 |
| 11 | 33553 |
| 12 | 87841 |
| 13 | 229971 |
| 14 | 602070 |
| 15 | 1576240 |
| 16 | 4126648 |
| 17 | 10803705 |
| 18 | 28284465 |
| 19 | 74049691 |
| 20 | 193864606 |
| 21 | 507544128 |
| 22 | 1328767776 |
| 23 | 3478759201 |
| 24 | 9107509825 |
| 25 | 23843770275 |
| 26 | 62423800998 |
| 27 | 163427632720 |
[1,3,6,16,40,105,273,715,1870,4896,12816,33553, 87841,229971,602070,1576240,4126648,10803705, 28284465,74049691,193864606,507544128,1328767776, 3478759201,9107509825,23843770275,62423800998, 163427632720] |