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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 40 |
| 5 | 120 |
| 6 | 356 |
| 7 | 1050 |
| 8 | 3088 |
| 9 | 9069 |
| 10 | 26620 |
| 11 | 78133 |
| 12 | 229384 |
| 13 | 673699 |
| 14 | 1979628 |
| 15 | 5820195 |
| 16 | 17121312 |
| 17 | 50394579 |
| 18 | 148413996 |
| 19 | 437324919 |
| 20 | 1289330520 |
| 21 | 3803175474 |
| 22 | 11223840012 |
| 23 | 33139076292 |
| 24 | 97889042384 |
| 25 | 289276841475 |
| 26 | 855205791076 |
| 27 | 2529279459099 |
[1,4,13,40,120,356,1050,3088,9069,26620,78133, 229384,673699,1979628,5820195,17121312,50394579, 148413996,437324919,1289330520,3803175474, 11223840012,33139076292,97889042384,289276841475, 855205791076,2529279459099] |