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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 21 |
| 3 | 112 |
| 4 | 615 |
| 5 | 3432 |
| 6 | 19383 |
| 7 | 110448 |
| 8 | 633726 |
| 9 | 3656360 |
| 10 | 21191555 |
| 11 | 123286440 |
| 12 | 719539015 |
| 13 | 4210967880 |
| 14 | 24702429825 |
| 15 | 145210795200 |
| 16 | 855172338570 |
| 17 | 5044470461352 |
| 18 | 29799593861974 |
| 19 | 176268499363840 |
| 20 | 1043889366927771 |
| 21 | 6188748520285584 |
| 22 | 36726461258947569 |
| 23 | 218146172715259488 |
| 24 | 1296812014083995850 |
[1,4,21,112,615,3432,19383,110448,633726,3656360, 21191555,123286440,719539015,4210967880, 24702429825,145210795200,855172338570, 5044470461352,29799593861974,176268499363840, 1043889366927771,6188748520285584, 36726461258947569,218146172715259488, 1296812014083995850] |