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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 20 |
| 3 | 80 |
| 4 | 264 |
| 5 | 809 |
| 6 | 2506 |
| 7 | 8432 |
| 8 | 30362 |
| 9 | 109520 |
| 10 | 391836 |
| 11 | 1408127 |
| 12 | 5002188 |
| 13 | 17308136 |
| 14 | 59463783 |
| 15 | 210199210 |
| 16 | 774578726 |
| 17 | 2918410859 |
| 18 | 10951007498 |
| 19 | 40430881133 |
| 20 | 146973680685 |
| 21 | 527988483182 |
| 22 | 1880363101497 |
| 23 | 6679919969564 |
| 24 | 23928818399537 |
[4,20,80,264,809,2506,8432,30362,109520,391836, 1408127,5002188,17308136,59463783,210199210, 774578726,2918410859,10951007498,40430881133, 146973680685,527988483182,1880363101497, 6679919969564,23928818399537] |