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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 280 |
| 6 | 1119 |
| 7 | 4596 |
| 8 | 19322 |
| 9 | 82650 |
| 10 | 358876 |
| 11 | 1576911 |
| 12 | 7001693 |
| 13 | 31358107 |
| 14 | 141524444 |
| 15 | 642918451 |
| 16 | 2937880585 |
| 17 | 13493909464 |
| 18 | 62267058197 |
| 19 | 288513529181 |
| 20 | 1341856939676 |
| 21 | 6261982534246 |
| 22 | 29313304996458 |
| 23 | 137606976791765 |
| 24 | 647659389106798 |
| 25 | 3055539614439363 |
| 26 | 14447445331063563 |
| 27 | 68451237108563191 |
[1,2,6,20,73,280,1119,4596,19322,82650,358876, 1576911,7001693,31358107,141524444,642918451, 2937880585,13493909464,62267058197,288513529181, 1341856939676,6261982534246,29313304996458, 137606976791765,647659389106798,3055539614439363, 14447445331063563,68451237108563191] |