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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 63 |
| 4 | 244 |
| 5 | 934 |
| 6 | 3549 |
| 7 | 13428 |
| 8 | 50694 |
| 9 | 191216 |
| 10 | 721259 |
| 11 | 2722073 |
| 12 | 10282610 |
| 13 | 38886330 |
| 14 | 147243585 |
| 15 | 558279000 |
| 16 | 2119599270 |
| 17 | 8058312360 |
| 18 | 30677134380 |
| 19 | 116937340494 |
| 20 | 446317079712 |
| 21 | 1705563385196 |
| 22 | 6525404350306 |
| 23 | 24994411455928 |
[1,4,16,63,244,934,3549,13428,50694,191216,721259, 2722073,10282610,38886330,147243585,558279000, 2119599270,8058312360,30677134380,116937340494, 446317079712,1705563385196,6525404350306, 24994411455928] |