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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 18 |
| 3 | 97 |
| 4 | 564 |
| 5 | 3512 |
| 6 | 23000 |
| 7 | 155611 |
| 8 | 1077871 |
| 9 | 7603553 |
| 10 | 54400028 |
| 11 | 393615806 |
| 12 | 2874398515 |
| 13 | 21151907950 |
| 14 | 156661034233 |
| 15 | 1166746786182 |
| 16 | 8731188863470 |
| 17 | 65612899915304 |
| 18 | 494890204904784 |
| 19 | 3745011184713964 |
| 20 | 28423094496953330 |
| 21 | 216289611853439384 |
| 22 | 1649819700464785589 |
[0,4,18,97,564,3512,23000,155611,1077871,7603553, 54400028,393615806,2874398515,21151907950, 156661034233,1166746786182,8731188863470, 65612899915304,494890204904784,3745011184713964, 28423094496953330,216289611853439384, 1649819700464785589] |