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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 19 |
| 4 | 68 |
| 5 | 255 |
| 6 | 1020 |
| 7 | 4221 |
| 8 | 18186 |
| 9 | 80304 |
| 10 | 364476 |
| 11 | 1684782 |
| 12 | 7944156 |
| 13 | 37988379 |
| 14 | 184406508 |
| 15 | 905147815 |
| 16 | 4495346570 |
| 17 | 22527055980 |
| 18 | 113957354940 |
| 19 | 580759868910 |
| 20 | 2982724210440 |
| 21 | 15414453711930 |
| 22 | 80177422383240 |
| 23 | 419249099692710 |
| 24 | 2204316120027420 |
| 25 | 11642676960438000 |
[1,2,6,19,68,255,1020,4221,18186,80304,364476, 1684782,7944156,37988379,184406508,905147815, 4495346570,22527055980,113957354940,580759868910, 2982724210440,15414453711930,80177422383240, 419249099692710,2204316120027420, 11642676960438000] |