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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 18 |
| 5 | 52 |
| 6 | 142 |
| 7 | 397 |
| 8 | 1098 |
| 9 | 3051 |
| 10 | 8460 |
| 11 | 23480 |
| 12 | 65140 |
| 13 | 180749 |
| 14 | 501498 |
| 15 | 1391483 |
| 16 | 3860822 |
| 17 | 10712348 |
| 18 | 29722698 |
| 19 | 82469313 |
| 20 | 228821202 |
| 21 | 634892599 |
| 22 | 1761587480 |
| 23 | 4887741040 |
| 24 | 13561638120 |
| 25 | 37628431801 |
| 26 | 104404708402 |
| 27 | 289683694927 |
[0,1,2,7,18,52,142,397,1098,3051,8460,23480,65140, 180749,501498,1391483,3860822,10712348,29722698, 82469313,228821202,634892599,1761587480, 4887741040,13561638120,37628431801,104404708402, 289683694927] |