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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 65 |
| 4 | 268 |
| 5 | 1120 |
| 6 | 4737 |
| 7 | 20244 |
| 8 | 87280 |
| 9 | 379073 |
| 10 | 1656348 |
| 11 | 7272896 |
| 12 | 32060673 |
| 13 | 141775396 |
| 14 | 628505296 |
| 15 | 2791696705 |
| 16 | 12419264300 |
| 17 | 55315472416 |
| 18 | 246607247233 |
| 19 | 1100229683508 |
| 20 | 4911436984752 |
| 21 | 21934428189121 |
| 22 | 97992663440444 |
[1,4,16,65,268,1120,4737,20244,87280,379073, 1656348,7272896,32060673,141775396,628505296, 2791696705,12419264300,55315472416,246607247233, 1100229683508,4911436984752,21934428189121, 97992663440444] |