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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 224 |
| 5 | 2346 |
| 6 | 28516 |
| 7 | 391042 |
| 8 | 5936376 |
| 9 | 98435034 |
| 10 | 1765073308 |
| 11 | 33962477610 |
| 12 | 696914830952 |
| 13 | 15174458669522 |
| 14 | 349117545211884 |
| 15 | 8456730834434722 |
| 16 | 215014409153234928 |
| 17 | 5722673988023673970 |
| 18 | 159062075672724943220 |
[1,1,4,26,224,2346,28516,391042,5936376,98435034, 1765073308,33962477610,696914830952, 15174458669522,349117545211884,8456730834434722, 215014409153234928,5722673988023673970, 159062075672724943220] |