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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 16 |
| 4 | 45 |
| 5 | 131 |
| 6 | 393 |
| 7 | 1218 |
| 8 | 3887 |
| 9 | 12736 |
| 10 | 42707 |
| 11 | 146113 |
| 12 | 508610 |
| 13 | 1796848 |
| 14 | 6428953 |
| 15 | 23253209 |
| 16 | 84893617 |
| 17 | 312435085 |
| 18 | 1157899672 |
| 19 | 4317354453 |
| 20 | 16183476500 |
| 21 | 60947573729 |
| 22 | 230481995102 |
| 23 | 874810511970 |
| 24 | 3331322503398 |
| 25 | 12723257204883 |
| 26 | 48722782351656 |
| 27 | 187028551724723 |
[1,2,6,16,45,131,393,1218,3887,12736,42707,146113, 508610,1796848,6428953,23253209,84893617, 312435085,1157899672,4317354453,16183476500, 60947573729,230481995102,874810511970, 3331322503398,12723257204883,48722782351656, 187028551724723] |