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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 15 |
| 3 | 80 |
| 4 | 609 |
| 5 | 4015 |
| 6 | 27936 |
| 7 | 190385 |
| 8 | 1307775 |
| 9 | 8956144 |
| 10 | 61405905 |
| 11 | 420831071 |
| 12 | 2884553280 |
| 13 | 19770670945 |
| 14 | 135511114479 |
| 15 | 928804587920 |
| 16 | 6366127657281 |
| 17 | 43634071586575 |
| 18 | 299072419071840 |
| 19 | 2049872742473489 |
| 20 | 14050037090947935 |
| 21 | 96300386075488816 |
| 22 | 660052667580788145 |
[0,1,15,80,609,4015,27936,190385,1307775,8956144, 61405905,420831071,2884553280,19770670945, 135511114479,928804587920,6366127657281, 43634071586575,299072419071840,2049872742473489, 14050037090947935,96300386075488816, 660052667580788145] |