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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 25 |
| 5 | 151 |
| 6 | 541 |
| 7 | 1471 |
| 8 | 84001 |
| 9 | 925345 |
| 10 | 5682601 |
| 11 | 25177681 |
| 12 | 2245355641 |
| 13 | 35901100951 |
| 14 | 312222474565 |
| 15 | 1917363070351 |
| 16 | 232479594721921 |
| 17 | 4873115730725761 |
| 18 | 54830346428307601 |
| 19 | 430468886732009185 |
| 20 | 65997947903313461401 |
| 21 | 1711564302775814535511 |
[1,1,1,1,25,151,541,1471,84001,925345,5682601, 25177681,2245355641,35901100951,312222474565, 1917363070351,232479594721921,4873115730725761, 54830346428307601,430468886732009185, 65997947903313461401,1711564302775814535511] |