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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 15 |
| 2 | 153 |
| 3 | 1431 |
| 4 | 13041 |
| 5 | 117855 |
| 6 | 1062153 |
| 7 | 9563751 |
| 8 | 86086881 |
| 9 | 774821295 |
| 10 | 6973509753 |
| 11 | 62761942071 |
| 12 | 564858541521 |
| 13 | 5083730062335 |
| 14 | 45753580126953 |
| 15 | 411782249840391 |
| 16 | 3706040334656961 |
| 17 | 33354363270192975 |
| 18 | 300189270206577753 |
| 19 | 2701703434183722711 |
| 20 | 24315330914627073201 |
[1,15,153,1431,13041,117855,1062153,9563751, 86086881,774821295,6973509753,62761942071, 564858541521,5083730062335,45753580126953, 411782249840391,3706040334656961, 33354363270192975,300189270206577753, 2701703434183722711,24315330914627073201] |