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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 61 |
| 4 | 652 |
| 5 | 5048 |
| 6 | 33152 |
| 7 | 197248 |
| 8 | 1098752 |
| 9 | 5838848 |
| 10 | 29949952 |
| 11 | 149454848 |
| 12 | 729546752 |
| 13 | 3497525248 |
| 14 | 16517169152 |
| 15 | 77015810048 |
| 16 | 355207217152 |
| 17 | 1622826549248 |
| 18 | 7352984010752 |
| 19 | 33073395662848 |
| 20 | 147798414589952 |
| 21 | 656648959950848 |
[0,4,61,652,5048,33152,197248,1098752,5838848, 29949952,149454848,729546752,3497525248, 16517169152,77015810048,355207217152, 1622826549248,7352984010752,33073395662848, 147798414589952,656648959950848] |