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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 9 |
| 4 | 42 |
| 5 | 120 |
| 6 | 570 |
| 7 | 1825 |
| 8 | 8890 |
| 9 | 30534 |
| 10 | 149418 |
| 11 | 536896 |
| 12 | 2650062 |
| 13 | 9848282 |
| 14 | 48696782 |
| 15 | 185458037 |
| 16 | 920584716 |
| 17 | 3576385528 |
| 18 | 17767869592 |
| 19 | 70107220264 |
| 20 | 348996559758 |
| 21 | 1395354752334 |
| 22 | 6949384790858 |
| 23 | 28086919632832 |
| 24 | 140041190373276 |
| 25 | 571375438865004 |
| 26 | 2849662081018354 |
| 27 | 11720152721264588 |
| 28 | 58492355525303946 |
[1,1,4,9,42,120,570,1825,8890,30534,149418,536896, 2650062,9848282,48696782,185458037,920584716, 3576385528,17767869592,70107220264,348996559758, 1395354752334,6949384790858,28086919632832, 140041190373276,571375438865004,2849662081018354, 11720152721264588,58492355525303946] |