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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 30 |
| 3 | 134 |
| 4 | 601 |
| 5 | 2665 |
| 6 | 11915 |
| 7 | 53134 |
| 8 | 237241 |
| 9 | 1058821 |
| 10 | 4726432 |
| 11 | 21096932 |
| 12 | 94170565 |
| 13 | 420346821 |
| 14 | 1876297370 |
| 15 | 8375198688 |
| 16 | 37384256688 |
| 17 | 166871556228 |
| 18 | 744862153097 |
| 19 | 3324830353450 |
| 20 | 14840996988230 |
| 21 | 66245542638609 |
| 22 | 295699266565050 |
[4,30,134,601,2665,11915,53134,237241,1058821, 4726432,21096932,94170565,420346821,1876297370, 8375198688,37384256688,166871556228,744862153097, 3324830353450,14840996988230,66245542638609, 295699266565050] |