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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 25 |
| 3 | 168 |
| 4 | 1229 |
| 5 | 9592 |
| 6 | 78498 |
| 7 | 664579 |
| 8 | 5761455 |
| 9 | 50847534 |
| 10 | 455052511 |
| 11 | 4118054813 |
| 12 | 37607912018 |
| 13 | 346065536839 |
| 14 | 3204941750802 |
| 15 | 29844570422669 |
| 16 | 279238341033925 |
| 17 | 2623557157654233 |
| 18 | 24739954287740860 |
| 19 | 234057667276344607 |
| 20 | 2220819602560918840 |
| 21 | 21127269486018731928 |
| 22 | 201467286689315906290 |
[0,4,25,168,1229,9592,78498,664579,5761455, 50847534,455052511,4118054813,37607912018, 346065536839,3204941750802,29844570422669, 279238341033925,2623557157654233, 24739954287740860,234057667276344607, 2220819602560918840,21127269486018731928, 201467286689315906290] |