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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 23 |
| 4 | 89 |
| 5 | 353 |
| 6 | 1471 |
| 7 | 6242 |
| 8 | 26712 |
| 9 | 116074 |
| 10 | 510008 |
| 11 | 2254425 |
| 12 | 10033860 |
| 13 | 44944615 |
| 14 | 202217909 |
| 15 | 913563797 |
| 16 | 4143671773 |
| 17 | 18855556442 |
| 18 | 86046484485 |
| 19 | 393738362852 |
| 20 | 1806026193866 |
| 21 | 8301731429786 |
| 22 | 38236965932111 |
| 23 | 176438461832407 |
| 24 | 815503547632070 |
| 25 | 3775140300273871 |
| 26 | 17501159489385700 |
| 27 | 81241736134010383 |
[1,2,6,23,89,353,1471,6242,26712,116074,510008, 2254425,10033860,44944615,202217909,913563797, 4143671773,18855556442,86046484485,393738362852, 1806026193866,8301731429786,38236965932111, 176438461832407,815503547632070,3775140300273871, 17501159489385700,81241736134010383] |