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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 42 |
| 3 | 288 |
| 4 | 1971 |
| 5 | 13674 |
| 6 | 95146 |
| 7 | 660556 |
| 8 | 4584620 |
| 9 | 31824915 |
| 10 | 220924781 |
| 11 | 1533614678 |
| 12 | 10646013585 |
| 13 | 73902329152 |
| 14 | 513014128876 |
| 15 | 3561233933988 |
| 16 | 24721320932489 |
| 17 | 171610099765915 |
| 18 | 1191280452221190 |
| 19 | 8269613020988031 |
| 20 | 57405877333497254 |
[4,42,288,1971,13674,95146,660556,4584620, 31824915,220924781,1533614678,10646013585, 73902329152,513014128876,3561233933988, 24721320932489,171610099765915,1191280452221190, 8269613020988031,57405877333497254] |